ZvT build order and strategy: Zerg vs Terraner

Checklist: do this

Open twelve hatchery, eleven pool: three hatcheries before four minutes and drones on every larva.
Spire by 4:30; nine to eleven mutalisks with scourge harass the main and keep bio at home.
Hydralisk den and lurkers as Terran's first push comes; lurkers hold the third base.
Fourth base and evolution chambers: carapace first, missile attacks after; upgrades keep lings and hydras relevant.
Lair to hive by 11:00; defiler mound and consume, then plague; ultralisk cavern after.
Drones to about sixty on four bases; more hatcheries than bases, always.
Overlords ahead of supply, spread across the map for vision, speed and sight when muta harass starts.
Scout Terran's opening with the drone and the overlord: two barracks, mech or a fast expansion each change your first fifteen units.

Why it works

Zerg cannot beat Terran bio unit for unit; it wins by having more bases and more larvae than Terran can pressure, and by making each Terran move-out cost time. Mutalisks harass so that marines stay home, lurkers hold the map while the third and fourth base saturate, and at hive the defiler turns bio into an army that cannot fight. The whole game is drones, then the right tech at the right time.

If you remember one sentenceThree hatcheries and drones, mutalisks to keep the marines home, lurkers to hold your bases, and defilers with plague and swarm to win the late game.

The build

Supply9 Time1:00 Overlord Ahead of the cap; the second overlord scouts.
Supply12 Time1:50 Hatchery at the natural Twelve hatch is the standard economic opening.
Supply11 Time2:10 Spawning Pool After the hatchery; zerglings in time for a bunker rush.
Supply13 Time2:40 Extractor Gas for the lair and the spire.
Supply15 Time3:20 Third Hatchery Three hatcheries of larvae is the economy.
Supply17 Time3:40 Lair The spire needs it by 4:30.
Supply20 Time4:30 Spire Mutalisks by 6:00 with the first nine gathered at once.
Supply26 Time5:00 Second and third Extractor Mutalisks and scourge cost gas.
Supply36 Time6:00 Nine Mutalisks and Scourge Kill SCVs and marines that stray; keep bio at home.
Supply44 Time7:00 Hydralisk Den, Evolution Chamber Lurkers for the first push; carapace +1.
Supply50 Time8:00 Fourth Hatchery and third base Larvae and income for the hive game.
Supply60 Time9:00 Lurker Aspect, sunken colonies at the third Lurkers hold ground; sunkens hold the base while they move.
Supply80 Time11:00 Hive Defilers, adrenal glands and ultralisks.
Supply90 Time12:30 Defiler Mound, Consume, then Plague The unit that wins the late game.

Research, in this order

Metabolic Boost at the Spawning Pool
Fast zerglings surround marines and kill vultures; research it first when gas is available.
Lurker Aspect at the Hydralisk Den
Lurkers hold everything Terran sends until vessels arrive.
Carapace +1 at the Evolution Chamber
Marines with +1 weapons kill zerglings in fewer shots; carapace takes it back.
Pneumatized Carapace at the Lair
Overlord speed; overlords survive and see across the map.
Consume at the Defiler Mound
Defilers need energy from zerglings for every swarm and plague.
Plague at the Defiler Mound
Kills vessels and leaves marines with one hit point.
Adrenal Glands at the Spawning Pool
Hive zerglings with crack attack speed eat bio under swarm.
Missile Attacks +1 at the Evolution Chamber
Hydralisks and lurkers; second evolution chamber at hive.

The army, stage by stage

Opening
Zergling
Six zerglings, then drones; lings guard against a bunker rush.
Mutalisks
MutaliskScourgeZergling
Nine to eleven mutalisks in one group; scourge for vessels and dropships.
Lurkers
LurkerZerglingMutalisk
Lurkers at chokes, lings to flank, mutas keep harassing.
Hive
DefilerZerglingUltraliskLurker
Swarm on the front, plague on the bio ball, cracklings and ultralisks under it.

If you scout…

Two barracks before a command center

When The first drone scout

Do Six zerglings at once, a sunken colony at the natural, drones after.

Why Marines and SCVs at 3:30 break a natural with no defence; one sunken and lings hold it.

A factory and no academy (mech)

When 4:00 to 6:00

Do Mutalisks harass, then hydralisks with speed and range, expand faster; skip lurkers.

Why Vultures and tanks beat lurkers and zerglings; hydralisks in numbers with more bases beat mech.

Command center first (fast expansion)

When 2:30 to 3:00

Do Drone hard, take a fourth hatchery early, mutalisks on time.

Why A greedy Terran has nothing to punish you with; be greedier.

Bio moving out with tanks and vessels

When 9:00 onward

Do Lurkers at the chokes, lings flank, mutalisks or scourge on the vessels; do not fight in the open until defilers.

Why Bio with detection beats lurkers in the open; at chokes and under swarm it does not.

Many turrets and valkyries

When 6:00 to 8:00

Do Stop at nine mutalisks, switch to lurkers and drones, use mutas only to defend.

Why Valkyries and turrets make more mutalisks a waste of gas.

Counters

They have	You answer with
Marines and medics	Lurkers at chokes, defilers, zergling surrounds Bio wins even fights; it loses to swarm, plague and lurkers it cannot see.
Siege Tanks	Zerglings and mutalisks on them, ultralisks Tanks are helpless up close and to air.
Science Vessels	Scourge, plague Two scourge kill a vessel; plague strips its hit points.
Vultures	Fast zerglings, mutalisks Vultures die to speed zerglings that catch them.
Firebats	Hydralisks, lurkers Firebats splash zerglings; ranged units do not care.

The mistakes that lose this matchup

Too few drones
The sign Under thirty drones at 6:00.
The fix Drones on every larva until the mutalisks start; three hatcheries by 3:20.
Mutalisks lost to marines
The sign Nine mutalisks dead in one engagement.
The fix Harass workers and stragglers only; never fight a stimmed ball.
No lurkers when the push comes
The sign The third base falls at 9:00.
The fix Hydralisk den at 7:00, lurker aspect by 9:00, sunkens at the third.
Hive too late
The sign No defilers at 13:00 against a +2 army.
The fix Lair at 3:40, hive by 11:00, mound the moment it finishes.
Supply-blocked
The sign Larvae waiting on overlords.
The fix An overlord every time you are 8 supply from the cap; two at a time after 40.

By level

Newcomer

Learn the opening to three hatcheries and to make a drone from every larva until 5:00. Make overlords before the cap. Get mutalisks by 6:00 and use them only against workers. Get lurkers by 9:00 and put them where Terran must walk. Everything else can wait.

Learner

The build above within thirty seconds, muta harass that kills SCVs without losing mutalisks, lurkers holding the third, hive by 11:00 and the first defiler by 13:00. Scout the Terran opening and use the fork table.

Competitor

Mutalisk micro against marines, scourge on vessels before they irradiate, lurker and zergling flanks, defiler control under fire, and the crackling-ultralisk timing that ends games.