I found this in the US forum. I don't know if it's legal or not, but credit goes to MrMrCmmndsU for this guide:
This guide will also count on your opponent being the general high-division Terran player--the one that does the predictable build orders of TvZ and A-moves his deathball into your base and expects to win because of the supposed cost-effectiveness of Terran units. In short, your average Terran player is not always going to be pro-level. He will be stupid. And we will take advantage of that.
I will also be assuming you know how to handle your macro (spawn larva, spread creep). But even if it's not perfect, you should still do fine--your opponent is not perfect either.
DISCLAIMER: I do not expect you to read the whole thread. Just pick a stage of the game (early/mid/late) you have trouble with, and check the section if you can read anything useful. Information on countering the general terran builds is listed in the mid game section.
Early Game
Build Orders
How do you usually open? I hope not with a 6-pool (certainly not going to get you anywhere), or even a 10-pool (unless you scout some early cheese). If you're planning on not rushing your opponent, opening with anything less than a 13-pool wouldn't be recommended for the sake of your economy. Most Zerg players (like me!) love to fast expand, so we usually do some variant of 14 pool/15 Hatch or 14 Hatch/14 Pool. But I'd like to propose a different approach--delaying that Fast Expand.
9 Overlord
14 Spawning Pool
13 Extractor
15 Overlord
16 Queen
18/19 Zerglings or Drones (your preference)
20 or 21 Expand with Metabolic Boost researching
Queue second queen at main; after it's done tech to lair if possible while taking second gas.
"Why? That's going to put you economically behind!"
Perhaps, but delaying our expansion has several benefits:
1. It's much harder to defend 2 bases early against reaper harass--when the delayed expo is finally set up, metabolic boost will be near or already complete.
2. Less vulnerable to marine/bunker pushes at your natural.
3. With spawn larva, you can easily make up for the time lost not getting such an early hatch.
4. And most importantly, the early gas with the spawning pool, the no fast expand, and the few zerglings you'll produce will scare a somewhat competent Terran player into thinking you're going for a baneling bust.
Let's take a look at the last benefit. If you killed the scouting scv, your opponent will be left with two options when he sees a delayed expand: Either prepare for the bust, or proceed normally, with the threat of losing early to a well-executed bust. As most Terran players have been busted one time or another, they will probably begin constructing a Baneling-proof wall. How does this benefit you? First, it puts the Terran in a defensive posture. He'll be less inclined to go forward with his usual harass before he's confident his ramp is safe enough, allowing you to power drones--he may not harass at all if it means getting busted while he's to busy microing a reaper or hellion. Second, he'll have to invest somewhat in early marines, delaying his tech and encouraging him to use those marines (and add on more) in his army later on. Third, his tech buildings will all be at the front, trying to serve as a wall--with a scouting zergling, you can run up the ramp and see what tech path he's going instead of having to sacrifice an overlord very early.
Now that we're on the topic of scouting, let's go over what generally means what when scouting a terran base.
Scouting and Counters
Early on, I found that even when I scouted a Terran base, I usually had no idea what he was doing because I couldn't tell what buildings indicated what I should expect. Hopefully I can help some of you out who may be confused when building a counter to a certain build.
Barracks w/Tech Lab=Reapers or Marauders. Check back later and see if you get a marauder shooting at your zergling-if not, expect reapers to already be at your base. Speedlings on creep do well to fight off a small number of reapers--no need to build a spine crawler unless your opponent continues to send reapers at you. If he does mass reapers...well, pray he doesn't have the apm of LZGamer and throw down a roach warren and build as many as necessary.
Barracks w/Reactor + Factory=Hellion harass. He will be switching his add-ons soon if the factory is being constructed-check back later. Again, speedlings on creep are your best friend, and a spine crawler at your ramp (with a queen blocking the ramp) can deter them from getting into your main.
2 Barracks w/Reactor&Tech Lab=Expect a MM push early on, but you're probably safe from early harass barring the first reaper or two. Prepare for the MM push with 1 or 2 spinecrawlers and a handful of zerglings (or banelings if you like them).
Barracks + Factory w/Tech Lab=Either it's going to be blue-flame hellion late harass or drop, or an early push with marines, hellions, and siege tanks. Prepare 1 or 2 spinecrawlers for the latter; the former may require you to build a roach warren and a couple of spines at each base (although a lot of speedlings may be able to hold it off); an investment in blue-flame hints at your Terran opponent's later transition to pure mech
Barracks + Factory w/no add-ons=Usually indicates 1/1/1 build (Rax+Fact+Starport)--you should be wary of drops or banshees--later scouting will be necessary.
Will add on more as I can remember/be reminded of them.
Early Game Pushes
All early game pushes can be handled with a handful of speedlings and a couple of spinecrawlers. You will probably see some combinations like Marine/Hellion, Marauder/Hellion, or just Marine/Marauder. MM can be handled with speedlings alone (I always put a spine just in case), while the other two you may want to put down an extra spinecrawler or 2 down depending on the number of hellions he includes in his army.
Mid Game
Opening Mid Game
Congratulations! You've made it this far! Now you've reach the scariest part of the ZvT match-up: Mid game. When you can afford it throw down a Spire, continue to pump drones, and start to scout with that sacrificial overlord.
Scouting
Send in your sacrificial overlord sometime while you lair is morphing, or right after it completes. I also cannot stress enough how important it is to seize the Xel-Naga Towers with your zerglings--knowing when your opponent is coming and when his units are out of position is key.
3 Barracks w/2 Tech Labs & 1 Reactor + Starport w/ or w/out Reactor=MMM in it's finest form.
2 Barracks w/add-ons + Factory w/Tech Lab=Check the composition of his army too if you can. Otherwise it'll most likey indicate a strong Marine/Marauder/Tank push.
Starport w/Tech Lab=Banshees on the way, with possible cloak. Get a 3rd Queen, and consider getting an evo chamber and spores if you see double port with tech labs.
Starport w/Reactor=Viking harass. Keep your overlords near the center of your base, where you can defend with queens.
2/3 Factories w/2 Tech Labs & 1 Reactor=Pure mech. Hellions, Thors, and Tanks will greet you in awhile.
2 Barracks w/each add-on + 2 Factories w/Tech Labs + Starport w/ or w/out Reactor=Biomech. A mix of Marines, Marauders, Medivacs, Thors, and Siege Tanks.
Strategy
Your goal in mid game is to get your natural fully saturated, build a spire, research burrow, build an infestor pit, take your 3rd expo, throw down another hatchery at your main to support speedling production, and upgrade. Whewph! Sounds like a lot--I can rarely remember to do them all, but get in as many as you can.
Again, Zerg is the reactive race, but we have two tools at our disposal to force Terran to play the way we want. The first was minor, the threat of a baneling bust, that made our Terran opponent build more marines than he would want and to clump his tech buildings together so we could easily scout them. The second is Mutalisks.
The Spire is a NECESSITY. Unless your opponent is building Thors and only just Thors, building mutalisks even when your opponent has a ton of marines or a Thor or two is something I recommend. Why? It forces your opponent to build static D all around his base, delaying any push until he feels confident he's constructed a no-fly zone. It shuts down any Starport centered play (barring Battlecruisers...but let's not let him get those!) Also, your opponent's army now MUST include Marines or Thors (as Vikings are terrible against Mutalisks). If he doesn't build enough Marines or Thors, he will be punished by your mutalisks if all his anti-air is trashed when the battle begins.
The magic of Mutalisks is that it forces your typical Terran opponent to fall into these 3 builds: MMM w/ Tank Support, Pure Mech, or BioMech.
Dealing with MMM and Tank Support
You see he's going this build--how do you prepare? First off, research burrow. You are going to rely on the fact that your average Terran player usually scans a position a bit forward of your natural to see your army composition--not at the ramp, or at a Xel-Naga tower that is on the way to your natural. Place your banelings there, but do NOT burrow your entire army. If he's reasonably smart, he'll think something's fishy, and either not push, scan at the ramp, or wait for a Raven.
On a side-note, you should never have to worry about a Raven in your first baneling-mine ambush. The 200 gas is a deterrent for many Terran players--It means almost 2 less tanks, or 8 less marauders, or 2 less medivacs. Later on, you won't be relying on baneling-mines to take out the bioball--consecutive fungal growths toast the marines, leaving just marauders and tanks to die to speedlings/mutas.
An early push with MMM & Tanks can come before you get infestors, leaving you with zerglings/banelings/mutalisks. If for some reason your burrow ambushed fails, you must resort to catching your opponent out of position. Place a few spinecrawlers (3-4) at a forward position near your natural. Your Terran opponent is not a pro. He will be impatient. Either he will siege all his tanks up at once and hit your spinecrawlers, or siege his tanks just out of range and a-move his bioball into your spines. In response to the former, move back your spinecrawlers, wait for his siege tanks to unsiege, and a-move your zergling/baneling/mutalisk ball into his. Without tanks to blow away the first wave of speedlings and banelings, you can quickly get a surround off his bioball, and force him to either siege up his tanks (causing his own bioball to get hit by splash) or leave them in unsieged form, where they are effectively useless against a swarm of lings. For the latter, again, A-move your ball into his. His tanks will not get to exploit their high range before your lings/blings close in, while your spines will also be helping you in the fight.
What could make staving off this early push easier? Grouping around 20 of your lings when you see the army moving towards you, and using them to flank your opponent when his tanks unsiege or his bioball moves in. Set your spinecrawlers up so the battle will be fought in a generally open area. The Bioball is strong against your speedling/baneling/mutalisk force only because of the tanks ability to exploit their range. Do not engage his army when his bioball surrounds the sieged tanks. Only when they move away from their tank support or unsiege is a good time to strike.
It doesn't take perfect positioning. It doesn't take careful micro of all your units. You don't even have to fight on creep (although preferred) if you can get a good surround because your army is so fast. Fighting this army composition is all about patience and knowing when to strike. If you can handle that, it'll simply be A-move versus A-move in your favor, given your army isn't severly outnumbered. And if you baneling mine was successful, it'll just be clean-up.
Dealing with Pure Mech
Pure Mech is all factory units: Blue-Flame Hellions, Thors, and Siege Tanks. Blue-Flame Hellions will give your zerglings trouble, especially if there are many of them and you can't get good positioning. Instead, you must get roaches. Because Pure Mech requires a ton of start-up, you shouldn't have to worry about a major push early. By then, you will have infestors out.
The same strategy applies when combatting any of these three builds. Either surround if the tanks are sieged, or attack head on when the tanks are not. When fighting a pure mech army, creep spread is far more important, because your roaches are so slow. Your composition should be speedlings (less or more depending on the number of hellions)/Roaches/Mutalisks (less or more depending on the Thor spam)/Infestors (4 should be enough).
A quick note on Mutalisks when facing Thors. When you A-move mutalisks, they tend to stack very nicely for the Thor's anti-air. Here's a tip for when you fight Thors in either harass or an engagment with mutalisks: instead of a-moving or right-clicking your mutas, give them a move command past the Thor, and when the bunch is right over them, THEN right-click the Thor you want to focus. Your mutalisks will remain in their unbunched formation, as they tend not to stack while moving, and you'll save a few mutas from splash. But microing your infestors should be your first priority, so if you don't have the APM to pull that off, don't worry about it too much.
As always, your army can win in a frontal assault as long as you engage at the correct time (and not at a choke). Well before he gets into position overlooking your natural (basically while his army is moving), harass his hellions with fungal growth; on creep, they will not be fast enough to catch your infestor, and you can just drop another fungal growth if anything tries to run up to you. When he's about to get into position, A-move your ball in, and prepare to keep your infestors casting. Fungal his hellions again, mind control a thor or two, and drop infested Terran everywhere. You will make him panic. He must siege his tanks to pick off your infestors, but that gives your roaches ample time to run through the hellions and thors without siege tank blasts being rained down on them. You're also not relying entirely on neural parasite to win the battle--infested terran with their relatively high dps and expendability thrown all around his units will get his own units spashed by the tanks. A pack of overlords thrown in will add to the chaos, and might even block his tanks from focusing on your infestors if you're careful.
Suppose he is already sieged up and in position? You must surround, or gamble that he will not focus down your infestors who are neural parasiting. Be patient. Only resort to A-moving your army into a positioned pure mech army if you must, and hope your opponent isn't smart enough to focus down infestors.
What could make combatting Pure Mech easier? Burrowed roaches and ambushing him before he gets into position or even if he is in position can quickly turn the battle in your favor when your infestors add to the chaos. Buying more time with speedling harass and muta harass can allow you to pump out more roaches/set up a good position/let your infestors store up more energy. Having the 2 infestors spawning Infested Terran burrow.
Dealing with BioMech
Biomech is one of the strongest terran compositions you can face, combining elements of MMM and Pure Mech into one super ball of Zerg hate. Marine/Marauder/Medivac/Hellion/Thor/Tank is the composition you will expect. However, depending on when he pushes, he may be lacking in a certain element (usually hellions). Exploit this.
As he mixed his composition with units from the first two builds, you will have to mix up your own army to take his on. Even though most Terran drop hellions in their early BioMech pushes (even in their late game ones), we will assume he does have hellions to combat your speedling army. Check his composition with a sacrificial overlord, and tailor your speedling/roach numbers according to his hellion/marauder numbers. Banelings are not a must, but certainly useful when fighting the bioball element of Biomech (and it is still possible to catch his army with mines if this is his first push). Mutalisks will not enjoy the serving of both marines and thors, but they are necessary too. And, as usualy infestors are a requirement to winning against any terran army.
The BioMech army is just as immobile as pure mech. While he approaches, get some consecutive fungal growths on his marines/marauders/hellions. If you can kill a large clump of the marines and damage the hellions, your speedlings will rip through the remaining marauders, thors, and tanks, and your mutalisks may not fall as fast. BioMech means that he will not have as many thors for anti-air, relying on marines instead. Punish him for that with your AOE, while neuraling the few thors that are in his army.
Try not to do a frontal engagement even if you can get a surround on BioMech before you can damage his marines with fungal growth. The great thing about fungal growth is, that a 55 HP combat shielded marine will take 36 damage over 6 seconds, and then lose 10 health to stim-leaving him with only 9 health (2 zergling hits) if he dares to stim when you engage. Fungaling his marines will delay his push to heal up, allowing you time to bolster your army. Or if he's stupid enough to push when his marines are still at less than half health, you can just drop another fungal on them and a-move into his ball, even if his tanks are in position, given you aren't hitting a choke.
What could make assaulting BioMech easier? Creep of course is recommended, but your army is fairly mobile if you didn't need roaches for his hellions. BioMech is susceptible to weaknesses from both compositions, allowing you to AOE his infantry, mind control his meat shields, and bomb his blob of low hp units.
What About Ghosts?
Ghosts can ruin your infestors day, sniping those neuraling and emp-ing the blob of them. The good thing is, infestors are fat, and many of them don't occupy the EMP area at a given time, allowing some to throw infested terrans/FG everywhere, as snipe makes neural to risky. Ghosts are also an incredibly expensive investment, 150/150, meaning every ghost means one less tank and marauder or almost one less Thor gas wise. Only late game, when your Terran opponent has enough bases to afford adding ghosts to his army without weakening it greatly do you have to fear them. And that's only when you face the rare Terran opponent who bothers to build them.
Maintain Map Control As You Proceed into Late Game
Keep your overlords around prospective expansions if you can remember; better yet, if you are fighting a MMM army or BioMech army, used burrowed zerglings to check for expansions. Do NOT burrow them right where the CC would be placed. No need to tell him that you know where he's expanding just yet--show him you know when 50 zerglings run into the expansion. Burrow the ling near the patch instead. If you're a fan of drops and nydus worms, use them to harass--but be wary that a couple of sensor towers will ruin your chance to surprise him.
Late Game
When the Tables Turn
You've defended against the first major push without crushing losses. As soon as you mop up, tech to Hive, expand if you haven't, and prepare for either the second game-deciding push or actually attacking the Terran. Your enemy's composition will most likey be the same, just larger, but you will have the choice of adding either the Broodlord or Ultralisk to strengthen your composition and take the fight to him.
Ultralisk or Broodlord?
Our Tier 3 consists of specialized, anti-ground units--one melee, one siege range. Many say the roles overlap--in many cases they do, but there are cases when you want to favor one over the other.
I've heard this a lot from both Terran and Zerg players: "Once you get to tier 3 and Ultralisks, you win, cuz Ultralisks pwn the @!#$@ out of all terran ground." Wrong. Watch the Idra vs Drewbie game, and watch as Idra masses ultras and expects them to win against a BioMech army that consisted of Marauders, Thors, and Siege Tanks. Even at one point, where he pulled off a flank, his ultras still got eaten alive by stimmed marauders and thors. Never, ever, ever build solely ultralisks against an army that consists of purely marauder, thors, and siege tanks--unless you get the perfect surround and already have the advantage in army size, you will be wasting money. At least throw in some zerglings (a good 60-80 of them to complement your ultras, and always engage in good places (Idra continued to assault at chokepoints). As melee units, you need to surround your opponents army, and with the current map pool, it's hard to find a spot where there is more than 3 paths to attack your enemy.
Which leaves us with Broodlords. Adding Broodlords to your mix when facing MMM with tank support means only marines can attack you. Fungal Growth the marines, and you annihilate their army. Facing Pure Mech with Broodlords means only the Thors can attack your Broodlords, and if you spread them, Thors won't do enough damage before your Broodlords AND ground army destroy him. Facing BioMech means you have marines that can't attack your Broodlords because of FG, and only half the Thors shooting your Broodlords than you would have if he had just gone Pure Mech. The only way he can fight off your broodlords is with enough vikings, and to build enough to stop your Broodlords could would mean weakening his ground army numbers to where your ground army would overwhelm them. You already had the tools at Tier 2 to shut down the MMM/Tank, Pure Mech, and BioMech army. Broodlords are an added bonus--you force him to weaken his ground army even more just to deal with the Broodlords.
Then when would Ultralisks ever be helpful? I suppose if your opponent built just Vikings and Thors, you could have Ultras complement your zerglings. Even then, fungal growth+Spam infested terran under vikings destroys them just as well. If your opponent is fond of ghosts and snipe, perhaps then you would prefer Ultras to Broodlords. Mass Mass Marines in an open area might call for ultras if you can't FG all the marines. Siege Tanks with Battlecruiser support (REALLY late game here) would favor Ultras because they don't die by one yamato cannon. Otherwise, in a map pool that favors nice chokes and narrow passages for the Terran ranged army, Broodlords are almost always a safe bet.
Congrats! You won!
People love to say that it takes a ton more micro and skill to effectively combat a Terran army with a Zerg composition. While that might be true, proper use of Infestors can easily swing the tide in your favor, whether it be a simple "F" on a BioBall, "E" on a Thor, and "T" for the rest--allowing your army to successfully A-move into his ball and come out victorious without the need for some careful flank or surprise unburrow. Patience and striking when your opponent is on the move--these aren't difficult tactics for anyone to master.
My Views on the ZvT Balance and Why I Think Zerg is Superior as a Reactive Race
For me as a Zerg, early game is hellish. While our race has few options beginning the game, to bust or not to bust and then to expand or fast expand, Terran can plan to go bunker & marine/reaper expansion denial, just reapers, 4 hellion reactor harass, banshees, thor drop, tank/marine drop, blue-flame hellion drop, marine/hellion push, viking overlord hunting, etc etc etc... many builds that are dangerous left unscouted. However, if we manage to get to the mid or late game mostly unscathed, and balance our drone/army count well based on careful scouting, our ability to create an army tailored any way we want instantly is incredible.
Terran, to keep competitive army wise, must always be building an army. We can spawn half an army in 2 rounds of spawn larva on both hatches, if we must. I scout my Terran opponent's army, almost assembled. I quickly construct an army that will counter his army if used correctly. Now, let's look through a Terran's point of view. They scout my army, hinting somewhat at the composition I've been building up (but can change in a matter of seconds). They realize I've been building up an army that shuts down there's, but because they HAVE to begin assembling an army early, they can choose to either switch techs from the army they've been constructing and get the counter units to the Zerg force, or continue building what they've been building. If they choose the former, they must delay their push to build sufficient counter units. Sure, Hellions counter zerglings, but for a force that consists of Thors, Marauders, and Siege Tanks, a few Hellions aren't going to stop Zerglings and Mutalisks from ripping that composition apart, and to get a nice critical mass of them (8-10) will buy the Zerg time to build an even larger army adapted to fight hellions. If they choose to do the latter and continue using their current build, they just get destroyed by more zerglings and more mutalisks.
As Zerg, we're not forced to slowly build up an army which can be scouted and have a counter force build against--we don't get stuck on tech paths that Terran and Protoss must commit to because half their army already consists of that build. With careful scouting, our army can never be countered for long--the ability to store up our production time through larva makes our race instantly adaptable on a scale the other two races don't have.
Again, I stress that the above guide is not from my own work, I've just copied and paste it from the US forum for SEA's benifit. I'm sure there are some that will have their own way of dealing with T, but I for one are one of those zergs that finds it hard to survive the early phase let alone late game, so please share. This is also the first guide that I've seen who actually advice players on a Terren's build base on what information you get from scouting, and I think that's the most important aspect on a zerg's game being reactive. Well, only need ZvP to complete this guide now.
This guide will also count on your opponent being the general high-division Terran player--the one that does the predictable build orders of TvZ and A-moves his deathball into your base and expects to win because of the supposed cost-effectiveness of Terran units. In short, your average Terran player is not always going to be pro-level. He will be stupid. And we will take advantage of that.
I will also be assuming you know how to handle your macro (spawn larva, spread creep). But even if it's not perfect, you should still do fine--your opponent is not perfect either.
DISCLAIMER: I do not expect you to read the whole thread. Just pick a stage of the game (early/mid/late) you have trouble with, and check the section if you can read anything useful. Information on countering the general terran builds is listed in the mid game section.
Early Game
Build Orders
How do you usually open? I hope not with a 6-pool (certainly not going to get you anywhere), or even a 10-pool (unless you scout some early cheese). If you're planning on not rushing your opponent, opening with anything less than a 13-pool wouldn't be recommended for the sake of your economy. Most Zerg players (like me!) love to fast expand, so we usually do some variant of 14 pool/15 Hatch or 14 Hatch/14 Pool. But I'd like to propose a different approach--delaying that Fast Expand.
9 Overlord
14 Spawning Pool
13 Extractor
15 Overlord
16 Queen
18/19 Zerglings or Drones (your preference)
20 or 21 Expand with Metabolic Boost researching
Queue second queen at main; after it's done tech to lair if possible while taking second gas.
"Why? That's going to put you economically behind!"
Perhaps, but delaying our expansion has several benefits:
1. It's much harder to defend 2 bases early against reaper harass--when the delayed expo is finally set up, metabolic boost will be near or already complete.
2. Less vulnerable to marine/bunker pushes at your natural.
3. With spawn larva, you can easily make up for the time lost not getting such an early hatch.
4. And most importantly, the early gas with the spawning pool, the no fast expand, and the few zerglings you'll produce will scare a somewhat competent Terran player into thinking you're going for a baneling bust.
Let's take a look at the last benefit. If you killed the scouting scv, your opponent will be left with two options when he sees a delayed expand: Either prepare for the bust, or proceed normally, with the threat of losing early to a well-executed bust. As most Terran players have been busted one time or another, they will probably begin constructing a Baneling-proof wall. How does this benefit you? First, it puts the Terran in a defensive posture. He'll be less inclined to go forward with his usual harass before he's confident his ramp is safe enough, allowing you to power drones--he may not harass at all if it means getting busted while he's to busy microing a reaper or hellion. Second, he'll have to invest somewhat in early marines, delaying his tech and encouraging him to use those marines (and add on more) in his army later on. Third, his tech buildings will all be at the front, trying to serve as a wall--with a scouting zergling, you can run up the ramp and see what tech path he's going instead of having to sacrifice an overlord very early.
Now that we're on the topic of scouting, let's go over what generally means what when scouting a terran base.
Scouting and Counters
Early on, I found that even when I scouted a Terran base, I usually had no idea what he was doing because I couldn't tell what buildings indicated what I should expect. Hopefully I can help some of you out who may be confused when building a counter to a certain build.
Barracks w/Tech Lab=Reapers or Marauders. Check back later and see if you get a marauder shooting at your zergling-if not, expect reapers to already be at your base. Speedlings on creep do well to fight off a small number of reapers--no need to build a spine crawler unless your opponent continues to send reapers at you. If he does mass reapers...well, pray he doesn't have the apm of LZGamer and throw down a roach warren and build as many as necessary.
Barracks w/Reactor + Factory=Hellion harass. He will be switching his add-ons soon if the factory is being constructed-check back later. Again, speedlings on creep are your best friend, and a spine crawler at your ramp (with a queen blocking the ramp) can deter them from getting into your main.
2 Barracks w/Reactor&Tech Lab=Expect a MM push early on, but you're probably safe from early harass barring the first reaper or two. Prepare for the MM push with 1 or 2 spinecrawlers and a handful of zerglings (or banelings if you like them).
Barracks + Factory w/Tech Lab=Either it's going to be blue-flame hellion late harass or drop, or an early push with marines, hellions, and siege tanks. Prepare 1 or 2 spinecrawlers for the latter; the former may require you to build a roach warren and a couple of spines at each base (although a lot of speedlings may be able to hold it off); an investment in blue-flame hints at your Terran opponent's later transition to pure mech
Barracks + Factory w/no add-ons=Usually indicates 1/1/1 build (Rax+Fact+Starport)--you should be wary of drops or banshees--later scouting will be necessary.
Will add on more as I can remember/be reminded of them.
Early Game Pushes
All early game pushes can be handled with a handful of speedlings and a couple of spinecrawlers. You will probably see some combinations like Marine/Hellion, Marauder/Hellion, or just Marine/Marauder. MM can be handled with speedlings alone (I always put a spine just in case), while the other two you may want to put down an extra spinecrawler or 2 down depending on the number of hellions he includes in his army.
Mid Game
Opening Mid Game
Congratulations! You've made it this far! Now you've reach the scariest part of the ZvT match-up: Mid game. When you can afford it throw down a Spire, continue to pump drones, and start to scout with that sacrificial overlord.
Scouting
Send in your sacrificial overlord sometime while you lair is morphing, or right after it completes. I also cannot stress enough how important it is to seize the Xel-Naga Towers with your zerglings--knowing when your opponent is coming and when his units are out of position is key.
3 Barracks w/2 Tech Labs & 1 Reactor + Starport w/ or w/out Reactor=MMM in it's finest form.
2 Barracks w/add-ons + Factory w/Tech Lab=Check the composition of his army too if you can. Otherwise it'll most likey indicate a strong Marine/Marauder/Tank push.
Starport w/Tech Lab=Banshees on the way, with possible cloak. Get a 3rd Queen, and consider getting an evo chamber and spores if you see double port with tech labs.
Starport w/Reactor=Viking harass. Keep your overlords near the center of your base, where you can defend with queens.
2/3 Factories w/2 Tech Labs & 1 Reactor=Pure mech. Hellions, Thors, and Tanks will greet you in awhile.
2 Barracks w/each add-on + 2 Factories w/Tech Labs + Starport w/ or w/out Reactor=Biomech. A mix of Marines, Marauders, Medivacs, Thors, and Siege Tanks.
Strategy
Your goal in mid game is to get your natural fully saturated, build a spire, research burrow, build an infestor pit, take your 3rd expo, throw down another hatchery at your main to support speedling production, and upgrade. Whewph! Sounds like a lot--I can rarely remember to do them all, but get in as many as you can.
Again, Zerg is the reactive race, but we have two tools at our disposal to force Terran to play the way we want. The first was minor, the threat of a baneling bust, that made our Terran opponent build more marines than he would want and to clump his tech buildings together so we could easily scout them. The second is Mutalisks.
The Spire is a NECESSITY. Unless your opponent is building Thors and only just Thors, building mutalisks even when your opponent has a ton of marines or a Thor or two is something I recommend. Why? It forces your opponent to build static D all around his base, delaying any push until he feels confident he's constructed a no-fly zone. It shuts down any Starport centered play (barring Battlecruisers...but let's not let him get those!) Also, your opponent's army now MUST include Marines or Thors (as Vikings are terrible against Mutalisks). If he doesn't build enough Marines or Thors, he will be punished by your mutalisks if all his anti-air is trashed when the battle begins.
The magic of Mutalisks is that it forces your typical Terran opponent to fall into these 3 builds: MMM w/ Tank Support, Pure Mech, or BioMech.
Dealing with MMM and Tank Support
You see he's going this build--how do you prepare? First off, research burrow. You are going to rely on the fact that your average Terran player usually scans a position a bit forward of your natural to see your army composition--not at the ramp, or at a Xel-Naga tower that is on the way to your natural. Place your banelings there, but do NOT burrow your entire army. If he's reasonably smart, he'll think something's fishy, and either not push, scan at the ramp, or wait for a Raven.
On a side-note, you should never have to worry about a Raven in your first baneling-mine ambush. The 200 gas is a deterrent for many Terran players--It means almost 2 less tanks, or 8 less marauders, or 2 less medivacs. Later on, you won't be relying on baneling-mines to take out the bioball--consecutive fungal growths toast the marines, leaving just marauders and tanks to die to speedlings/mutas.
An early push with MMM & Tanks can come before you get infestors, leaving you with zerglings/banelings/mutalisks. If for some reason your burrow ambushed fails, you must resort to catching your opponent out of position. Place a few spinecrawlers (3-4) at a forward position near your natural. Your Terran opponent is not a pro. He will be impatient. Either he will siege all his tanks up at once and hit your spinecrawlers, or siege his tanks just out of range and a-move his bioball into your spines. In response to the former, move back your spinecrawlers, wait for his siege tanks to unsiege, and a-move your zergling/baneling/mutalisk ball into his. Without tanks to blow away the first wave of speedlings and banelings, you can quickly get a surround off his bioball, and force him to either siege up his tanks (causing his own bioball to get hit by splash) or leave them in unsieged form, where they are effectively useless against a swarm of lings. For the latter, again, A-move your ball into his. His tanks will not get to exploit their high range before your lings/blings close in, while your spines will also be helping you in the fight.
What could make staving off this early push easier? Grouping around 20 of your lings when you see the army moving towards you, and using them to flank your opponent when his tanks unsiege or his bioball moves in. Set your spinecrawlers up so the battle will be fought in a generally open area. The Bioball is strong against your speedling/baneling/mutalisk force only because of the tanks ability to exploit their range. Do not engage his army when his bioball surrounds the sieged tanks. Only when they move away from their tank support or unsiege is a good time to strike.
It doesn't take perfect positioning. It doesn't take careful micro of all your units. You don't even have to fight on creep (although preferred) if you can get a good surround because your army is so fast. Fighting this army composition is all about patience and knowing when to strike. If you can handle that, it'll simply be A-move versus A-move in your favor, given your army isn't severly outnumbered. And if you baneling mine was successful, it'll just be clean-up.
Dealing with Pure Mech
Pure Mech is all factory units: Blue-Flame Hellions, Thors, and Siege Tanks. Blue-Flame Hellions will give your zerglings trouble, especially if there are many of them and you can't get good positioning. Instead, you must get roaches. Because Pure Mech requires a ton of start-up, you shouldn't have to worry about a major push early. By then, you will have infestors out.
The same strategy applies when combatting any of these three builds. Either surround if the tanks are sieged, or attack head on when the tanks are not. When fighting a pure mech army, creep spread is far more important, because your roaches are so slow. Your composition should be speedlings (less or more depending on the number of hellions)/Roaches/Mutalisks (less or more depending on the Thor spam)/Infestors (4 should be enough).
A quick note on Mutalisks when facing Thors. When you A-move mutalisks, they tend to stack very nicely for the Thor's anti-air. Here's a tip for when you fight Thors in either harass or an engagment with mutalisks: instead of a-moving or right-clicking your mutas, give them a move command past the Thor, and when the bunch is right over them, THEN right-click the Thor you want to focus. Your mutalisks will remain in their unbunched formation, as they tend not to stack while moving, and you'll save a few mutas from splash. But microing your infestors should be your first priority, so if you don't have the APM to pull that off, don't worry about it too much.
As always, your army can win in a frontal assault as long as you engage at the correct time (and not at a choke). Well before he gets into position overlooking your natural (basically while his army is moving), harass his hellions with fungal growth; on creep, they will not be fast enough to catch your infestor, and you can just drop another fungal growth if anything tries to run up to you. When he's about to get into position, A-move your ball in, and prepare to keep your infestors casting. Fungal his hellions again, mind control a thor or two, and drop infested Terran everywhere. You will make him panic. He must siege his tanks to pick off your infestors, but that gives your roaches ample time to run through the hellions and thors without siege tank blasts being rained down on them. You're also not relying entirely on neural parasite to win the battle--infested terran with their relatively high dps and expendability thrown all around his units will get his own units spashed by the tanks. A pack of overlords thrown in will add to the chaos, and might even block his tanks from focusing on your infestors if you're careful.
Suppose he is already sieged up and in position? You must surround, or gamble that he will not focus down your infestors who are neural parasiting. Be patient. Only resort to A-moving your army into a positioned pure mech army if you must, and hope your opponent isn't smart enough to focus down infestors.
What could make combatting Pure Mech easier? Burrowed roaches and ambushing him before he gets into position or even if he is in position can quickly turn the battle in your favor when your infestors add to the chaos. Buying more time with speedling harass and muta harass can allow you to pump out more roaches/set up a good position/let your infestors store up more energy. Having the 2 infestors spawning Infested Terran burrow.
Dealing with BioMech
Biomech is one of the strongest terran compositions you can face, combining elements of MMM and Pure Mech into one super ball of Zerg hate. Marine/Marauder/Medivac/Hellion/Thor/Tank is the composition you will expect. However, depending on when he pushes, he may be lacking in a certain element (usually hellions). Exploit this.
As he mixed his composition with units from the first two builds, you will have to mix up your own army to take his on. Even though most Terran drop hellions in their early BioMech pushes (even in their late game ones), we will assume he does have hellions to combat your speedling army. Check his composition with a sacrificial overlord, and tailor your speedling/roach numbers according to his hellion/marauder numbers. Banelings are not a must, but certainly useful when fighting the bioball element of Biomech (and it is still possible to catch his army with mines if this is his first push). Mutalisks will not enjoy the serving of both marines and thors, but they are necessary too. And, as usualy infestors are a requirement to winning against any terran army.
The BioMech army is just as immobile as pure mech. While he approaches, get some consecutive fungal growths on his marines/marauders/hellions. If you can kill a large clump of the marines and damage the hellions, your speedlings will rip through the remaining marauders, thors, and tanks, and your mutalisks may not fall as fast. BioMech means that he will not have as many thors for anti-air, relying on marines instead. Punish him for that with your AOE, while neuraling the few thors that are in his army.
Try not to do a frontal engagement even if you can get a surround on BioMech before you can damage his marines with fungal growth. The great thing about fungal growth is, that a 55 HP combat shielded marine will take 36 damage over 6 seconds, and then lose 10 health to stim-leaving him with only 9 health (2 zergling hits) if he dares to stim when you engage. Fungaling his marines will delay his push to heal up, allowing you time to bolster your army. Or if he's stupid enough to push when his marines are still at less than half health, you can just drop another fungal on them and a-move into his ball, even if his tanks are in position, given you aren't hitting a choke.
What could make assaulting BioMech easier? Creep of course is recommended, but your army is fairly mobile if you didn't need roaches for his hellions. BioMech is susceptible to weaknesses from both compositions, allowing you to AOE his infantry, mind control his meat shields, and bomb his blob of low hp units.
What About Ghosts?
Ghosts can ruin your infestors day, sniping those neuraling and emp-ing the blob of them. The good thing is, infestors are fat, and many of them don't occupy the EMP area at a given time, allowing some to throw infested terrans/FG everywhere, as snipe makes neural to risky. Ghosts are also an incredibly expensive investment, 150/150, meaning every ghost means one less tank and marauder or almost one less Thor gas wise. Only late game, when your Terran opponent has enough bases to afford adding ghosts to his army without weakening it greatly do you have to fear them. And that's only when you face the rare Terran opponent who bothers to build them.
Maintain Map Control As You Proceed into Late Game
Keep your overlords around prospective expansions if you can remember; better yet, if you are fighting a MMM army or BioMech army, used burrowed zerglings to check for expansions. Do NOT burrow them right where the CC would be placed. No need to tell him that you know where he's expanding just yet--show him you know when 50 zerglings run into the expansion. Burrow the ling near the patch instead. If you're a fan of drops and nydus worms, use them to harass--but be wary that a couple of sensor towers will ruin your chance to surprise him.
Late Game
When the Tables Turn
You've defended against the first major push without crushing losses. As soon as you mop up, tech to Hive, expand if you haven't, and prepare for either the second game-deciding push or actually attacking the Terran. Your enemy's composition will most likey be the same, just larger, but you will have the choice of adding either the Broodlord or Ultralisk to strengthen your composition and take the fight to him.
Ultralisk or Broodlord?
Our Tier 3 consists of specialized, anti-ground units--one melee, one siege range. Many say the roles overlap--in many cases they do, but there are cases when you want to favor one over the other.
I've heard this a lot from both Terran and Zerg players: "Once you get to tier 3 and Ultralisks, you win, cuz Ultralisks pwn the @!#$@ out of all terran ground." Wrong. Watch the Idra vs Drewbie game, and watch as Idra masses ultras and expects them to win against a BioMech army that consisted of Marauders, Thors, and Siege Tanks. Even at one point, where he pulled off a flank, his ultras still got eaten alive by stimmed marauders and thors. Never, ever, ever build solely ultralisks against an army that consists of purely marauder, thors, and siege tanks--unless you get the perfect surround and already have the advantage in army size, you will be wasting money. At least throw in some zerglings (a good 60-80 of them to complement your ultras, and always engage in good places (Idra continued to assault at chokepoints). As melee units, you need to surround your opponents army, and with the current map pool, it's hard to find a spot where there is more than 3 paths to attack your enemy.
Which leaves us with Broodlords. Adding Broodlords to your mix when facing MMM with tank support means only marines can attack you. Fungal Growth the marines, and you annihilate their army. Facing Pure Mech with Broodlords means only the Thors can attack your Broodlords, and if you spread them, Thors won't do enough damage before your Broodlords AND ground army destroy him. Facing BioMech means you have marines that can't attack your Broodlords because of FG, and only half the Thors shooting your Broodlords than you would have if he had just gone Pure Mech. The only way he can fight off your broodlords is with enough vikings, and to build enough to stop your Broodlords could would mean weakening his ground army numbers to where your ground army would overwhelm them. You already had the tools at Tier 2 to shut down the MMM/Tank, Pure Mech, and BioMech army. Broodlords are an added bonus--you force him to weaken his ground army even more just to deal with the Broodlords.
Then when would Ultralisks ever be helpful? I suppose if your opponent built just Vikings and Thors, you could have Ultras complement your zerglings. Even then, fungal growth+Spam infested terran under vikings destroys them just as well. If your opponent is fond of ghosts and snipe, perhaps then you would prefer Ultras to Broodlords. Mass Mass Marines in an open area might call for ultras if you can't FG all the marines. Siege Tanks with Battlecruiser support (REALLY late game here) would favor Ultras because they don't die by one yamato cannon. Otherwise, in a map pool that favors nice chokes and narrow passages for the Terran ranged army, Broodlords are almost always a safe bet.
Congrats! You won!
People love to say that it takes a ton more micro and skill to effectively combat a Terran army with a Zerg composition. While that might be true, proper use of Infestors can easily swing the tide in your favor, whether it be a simple "F" on a BioBall, "E" on a Thor, and "T" for the rest--allowing your army to successfully A-move into his ball and come out victorious without the need for some careful flank or surprise unburrow. Patience and striking when your opponent is on the move--these aren't difficult tactics for anyone to master.
My Views on the ZvT Balance and Why I Think Zerg is Superior as a Reactive Race
For me as a Zerg, early game is hellish. While our race has few options beginning the game, to bust or not to bust and then to expand or fast expand, Terran can plan to go bunker & marine/reaper expansion denial, just reapers, 4 hellion reactor harass, banshees, thor drop, tank/marine drop, blue-flame hellion drop, marine/hellion push, viking overlord hunting, etc etc etc... many builds that are dangerous left unscouted. However, if we manage to get to the mid or late game mostly unscathed, and balance our drone/army count well based on careful scouting, our ability to create an army tailored any way we want instantly is incredible.
Terran, to keep competitive army wise, must always be building an army. We can spawn half an army in 2 rounds of spawn larva on both hatches, if we must. I scout my Terran opponent's army, almost assembled. I quickly construct an army that will counter his army if used correctly. Now, let's look through a Terran's point of view. They scout my army, hinting somewhat at the composition I've been building up (but can change in a matter of seconds). They realize I've been building up an army that shuts down there's, but because they HAVE to begin assembling an army early, they can choose to either switch techs from the army they've been constructing and get the counter units to the Zerg force, or continue building what they've been building. If they choose the former, they must delay their push to build sufficient counter units. Sure, Hellions counter zerglings, but for a force that consists of Thors, Marauders, and Siege Tanks, a few Hellions aren't going to stop Zerglings and Mutalisks from ripping that composition apart, and to get a nice critical mass of them (8-10) will buy the Zerg time to build an even larger army adapted to fight hellions. If they choose to do the latter and continue using their current build, they just get destroyed by more zerglings and more mutalisks.
As Zerg, we're not forced to slowly build up an army which can be scouted and have a counter force build against--we don't get stuck on tech paths that Terran and Protoss must commit to because half their army already consists of that build. With careful scouting, our army can never be countered for long--the ability to store up our production time through larva makes our race instantly adaptable on a scale the other two races don't have.
Again, I stress that the above guide is not from my own work, I've just copied and paste it from the US forum for SEA's benifit. I'm sure there are some that will have their own way of dealing with T, but I for one are one of those zergs that finds it hard to survive the early phase let alone late game, so please share. This is also the first guide that I've seen who actually advice players on a Terren's build base on what information you get from scouting, and I think that's the most important aspect on a zerg's game being reactive. Well, only need ZvP to complete this guide now.