Blame Eric! It was him and his blog post about an old scifi-horror comic strip by Basil Wolverton that introduced me to the Brain-Bats of Venus. And this short, pulp-scifi exposure triggered what things like these often trigger with me. This one reaction: Hey, that would make a good Mutant Future(tm) creature!
DISCLAIMER: I did not stick to the ideas of Basil Wolverton but added my own as well.
No. Enc.: 1d4 (2d6)
Movement: 180´(60´) (Flying); or as host creature
Armor Class: 8
Attacks: 1; or as host creature
Damage: Special (see below); or as host creature
Hit Dice: 1; or as host creature
Hoard Class: None; or as host creature
Mutations/Powers: Parasitic Control (see below); Unique Sense (Brain Waves; 60´); Swarm Telepathy (60´); Quick Mind; No fine manipulators.
The Brain-Bats are a malign, intelligent species of mutants that look very much like a brain with eyes that grows out of manta ray or octopus with a 2 feet diameter. They enslave other beings to use their bodies as tools, and to steal their skills and memory. A brain-bat attacks to latch itself onto the head of its target (that is entitled to an Ability Test vs. Dexterity to dodge the attempt at the last minute). If the brain-bat is successful, its victim becomes stunned immediately as the creature begins to suppress its mind and takes control (which it achieves after two rounds unless attacked or separated; it counts as stunned as well). For an unknown reason, Brain-Bats need to be very close to another creature´s brain to gain control over it. After a turn (during which the creature just sucks itself to the host and clings to it) the Brain-Bat will insert dozens of fine, needle-like stingers into its host through which it takes nutrients from the creatures blood (and exists like a parasite). While attached, the creature has access to all knowledge, skills and powers the host has. A Brain-Bat is able to take over a fresh corpse the same way it can take over a living creatures body, but a corpse becomes useless after two days due to decay. Creatures without a (biological) brain cannot be taken over by Brain-Bats.Living creatures lose one point of CON every 2d6 days to the parasitic nature of the Brain-Bat.
If a brain-bat is attacked while it is attached to a victims head, the victim will suffer half of the damage the creature receives. Prying it off takes a successful check for Open Doors, and if the Brain-Bat was attached for a turn or longer the victim will take 1d4 damage as well. A victim that is freed has full memories of what it did and experienced as a Brain-Bat host.
Any Brain-Bat that is encountered has a 75% chance to be attached to a host (roll again for a random encounter to determine the host, re-roll results that make no sense), Brain-Bats encountered inside a lair will have a 50% chance to be attached to a host (and those without one will wait impatiently for their kinfolk to bring in new victims).