Epsilon Spook are... creatures, with a permanent bad temper due to the variety of experiments conducted on them and being the premier biological unit to be placed in Bio Reactors. Able to sniff out spies, maul infantry to death and traverse bodies of water, the spooky Spooks make great scouts.
Spooks fulfill a role that Yuri's army did not exactly have in the original Yuri's Revenge; a quick, cheap and amphibious scout in the early game able to chase down other Attack Dogs and tear lone infantry (especially Engineers) to shreds. Their ability to detect and kill infiltrators and other infantry instantly makes them important in all stages of a battle and combined with a Cloning Vats, they are able to outnumber infantry battalions and serve as cannon fodder as Viruses and Gatling weaponry finish off the remaining survivors.
Because they are the cheapest "infantry" of the Epsilon, they are the prime candidates for Bio Reactor placement. This common practice also deters the enemy from sending spies to sabotage the Epsilon base, as long as the proselyte is consistently aware of incoming spy operations and therefore release the Spooks within the Bio Reactors to hinder them.
Despite their appearance, they are statistically identical to Attack Dogs; therefore they share the same weaknesses, such as frail health and inability to harm certain infantry (especially Foehn ones), vehicles and structures (though the least the Spooks could do is become cannon fodder, as mentioned before).
- Spooks make their first appearance in The Conqueror. They have replaced Attack Dogs for Epsilon during the time period between the two acts.
- The Spook is a homage to the Facehugger from the Alien series.
- The Spook uses the voiceset of the in .