Born in a pit of death, filth, and disease, the Defiler is perhaps the most alarming and loathsome of all the Zerg breeds. This serpentine creature prospers under such conditions that all other forms of life find offensive and even deadly.

While this creature is weak in constitution, incapable of attacking its enemies directly, and not particularly quick, it possesses two abilities that make it a most powerful addition to the Zerg brood indeed. Though the Defiler cannot fight, it can burrow underground if endangered. It is also rather inexpensive to produce.

Dark Swarm
For 100 points of energy, a Defiler can propel a huge swarm of tiny insect-like creatures to a given point. The resulting cloud hangs in the air for a long while and absorbs all enemy ranged attacks, thus protecting those Zerg units underneath it from the harmful effects of projectile weapons. Of particular note is the fact that Dark Swarm negates virtually every type of Terran attack - Marines, Ghosts, Goliaths, Vultures, Wraiths, and Battlecruisers are all useless against units within the cloud. Only siege mode Siege Tanks and Firebats can successfully penetrate the cloud. Meanwhile, an enemy Zerg force using mostly Hydralisks and Mutalisks cannot breach the cloud. However, Dark Swarm is less useful against the Protoss, whose Zealots, Archons, and Reavers may all attack through the cloud uninhibited. But perhaps the true power of Dark Swarm is the fact that Zerg units within the cloud may still fight back with their typical ferocity. Thus Hydralisks within a Dark Swarm may devastate enemy flying units without any fear of retaliation. Dark Swarm hangs low to the ground, so it will not protect your own flying units from enemy firepower. But this is hardly a setback for an ability whose power must never be underestimated. Use Dark Swarm before raiding the enemy base, then burrow the Defiler out of sight.

Plague
You must research Plague at your Defiler Mound before you can use it. The designation "Plague" is a bit of a misnomer; when it uses this ability, the Defiler spits forth a thick, red, acidic toxin that coats all units and structures in a wide area and starts eating away at them at a fearsome rate. Plague costs 150 energy per use. Plague will never kill its target, but will atrophy up to 300 hit points or reduce it to one point of health, whichever comes first. Plague is perfect for hit-and-run strikes against an enemy base, as a preemptive attack against an enemy force or as a long-range means of damaging enemy defenses. Plague will also reveal any cloaked units caught within the attack. Plague does not affect Protoss Shields, but cuts straight to the hit points, bypassing shields altogether. Remember that Plague is just as dangerous to your forces as it is to the enemy, so make certain your warriors are nowhere near the Defiler's targeted area. Plague is particularly deadly when used against an enemy supply line. Reduce all the opponent's gatherer units to one hit point, then send in a few units - Mutalisks, with their ricocheting Glave Wurm attack, are perfect for the job - and destroy then.

Consume
After you research Consume from your Defiler Mound, you may order a Defiler to eat any of its brethren besides Larva. The nutrients from the unfortunate victim will restore 50 points of energy to the Defiler. While a Defiler may consume anything from an Ultralisk to a Mutalisk, it will always regain 50 energy and nothing more. For this reason, Zerglings are the obvious choice for consumption, since they cost a mere 50 minerals per pair. If you use Defilers often, follow them with packs of Zerglings that the Defilers can feast on to use Dark Swarm an Plague more frequently.

You may also evolve a Metasynaptic Node for your Defilers that increases maximum energy reserves by 50 points. This lets the Defiler use both Plague and Dark Swarm before resting.

Next: Scourge