Zerg Defiler

Overview

The Defiler looks similar to a giant silverfish. It is unknown what creature the Defiler was evolved from but regardless, it is an incredibly deadly Zerg breed. The Defiler contains the DNA of every Zerg species but unlike the Larva, which uses it to morph into Zerg units, the Defiler uses this DNA to manufacture hazardous biochemicals. The Defiler shows cannibalistic tendencies as it is necessary for the manufacturing of its biochemicals. Numerous small organisms live on the Defiler's carapace and the Defiler can launch these organisms to create a highly toxic swarm.

StarCraft

The Defiler was initially not used by Zerg players because it was considered "too APM intensive" to be of any use. However the Defiler is now a staple of the late game Zerg army, especially against Protoss. It is mainly used for its Dark Swarm ability. Dark Swarm makes ground units completely immune to every air unit and many ground units as well. Dark Swarm is invaluable for protecting Zerg forces especially the Zergling and the Ultralisk. Plague is not used as often as Dark Swarm but can be equally as effective. Plague can bring most units down to 1 HP and severely cripple Battlecruisers and Carriers. Plague is effectively combined with a single Mutalisk; thanks to its bouncing attack, the Mutalisk can kill three units per hit after Plague. Consume is the lynchpin of the Defiler, allowing it cast its spells almost indefinitely. Defilers are often accompanied by Zerglings as they serve as a cheap source of energy. The Metasynaptic Node, like all other energy upgrades, is useful for expanding the energy pool and increasing starting energy.

Against Protoss, the Defiler's Dark Swarm serves as its principle spell until the arrival of High Templars with Psionic Storm. Dark Swarm also only causes Archons to deal splash damage, cutting the Archon's power a bit. Without Dragoon and Archon support, the Zealots are decimated by Lurkers and Zerglings. Plague is also useful as many Protoss units have large amounts of hit points; Plague can effectively cut a Protoss army in half. Defilers are not as useful against either Archon as Archons are not particularly affected by either of the Defiler's spells and Dark Archons can snipe Defilers with Feedback. Reavers are also immune to Dark Swarm.

Against Terran, the Defiler's Dark Swarm negates Marine-Medic armies and forces Terrans to retreat. Plague is also incredibly useful against Marine-Medic as it causes Medics to waste energy trying to heal the Marines. If Terran incorporates Siege Tanks however, the Defiler isn't quite as useful as Dark Swarm doesn't protect splash damage and the Defiler is too frail to get up close and cast Plague. Should a Defiler manage to cast Plague on a group of Siege Tanks however, the battle can turn very quickly to the Zerg side. Firebats can attack through Dark Swarm but they are rarely used.

Due to the fast nature of the Zerg vs Zerg matchup, Defilers are rarely used as the match is often decided within ten minutes. Should the battle continue however, the Defiler's Plague is devastating to the Zerg Mutalisk air war.

Starcraft II

The Defiler has been replaced by the Infestor, which has a Plague like ability called Fungal Growth. The Defiler's Dark Swarm ability can be seen in the Terran Raven's Point Defense Drone ability. In the Starcraft II: Wings of Liberty campaign, the player can collect Defiler bones for Zerg research. Blizzard's Dustin Browder has stated the possibility of the Defiler appearing in the Zerg expansion, Starcraft II: Heart of the Swarm.