A large flea-based mutation, related to the Drain Deimos, albeit somewhat rarer and more intelligent, since it can stand up to attack the player with their claws.
Biology
The Brain Sucker shares many of the Drain Deimos behaviour patterns and abilities. They are, however, slightly stronger and possess the ability to spit poison at their prey. They are known to feed on the brains of their victims using their lock tongues, unlike the Drain Deimos, which fed on cerebra-spinal fluid. Their appearance is considerably more grotesque than their smaller cousins, possessing a sickly green colour, two heads and a musculature appearing to rip through their exoskeletons.
A Brain Sucker in Resident Evil 3: Nemesis