Objectives:
Destroy the Protoss Temple
The keys to this mission are resource management and choosing your battles. There are four Protoss bases: one to the west, one to the east, one around the temple and one to the north of the temple. Do not bother attacking the northern temple; you just need to destroy the temple, not all Protoss forces.
Begin by creating a lot of Drones (12+) to harvest resources. Gather as much as you can as fast as you can. Build a very heavy defense around your base; this is critical. The Protoss outnumber you heavily, making a good defense is essential in the early stages of the mission. Judicious application of upgrades can give you a good advantage. Only research the upgrades you know you will use. If you don’t use Zerglings much, don’t bother upgrading them. If you don’t use Defilers much, don’t even build a Defiler Mound. Use the resources instead to build and upgrade the units you do use.
Build Hydralisks, Mutalisks, Ultralisks and Guardians, in that order. Use them to attack the western base, then the eastern. Take the resource caches and set up secondary bases around them. Build good defenses (not necessarily gigantic defenses, but good ones) and continue building up your main assault force.
Build 24 Zerglings in addition to your main assault force. This is your “decoy force.” Send them in ahead of the main assault and let them get chewed up. While they are being torn apart, send your main attack force of Hydralisks, Mutalisks, Ultralisks and Guardians in for the kill. Eliminate Carriers, Reavers and Photon Cannons first. Then concentrate on Scouts, Dragoons and Zealots.
Continue pounding the Protoss until you have opened up a large enough hole in the main base to allow access to the Temple. Send part of your main assault force (at least four Guardians and an Ultralisk) to attack the temple while the rest of your troops continue to decimate the base. Keep units coming throughout the attack; your loses will most likely be high not due to your own fault but to the shear weight of enemies facing you. Keeping your units restocked with troops is imperative to the mission. It is advisable to build a couple extra Hives to keep production up. Once the temple is destroyed, the Zerg campaign is complete.