A Brain-Bat can slip onto a corpse and wear it like a zombie. Treat the corspe as a Zombie (DCC core rulebook, page 431), except that it attacks with a claw (1d4) or a weapon (by weapon type).
When a Brain-Bat is slain, its wail of psychic distress affects all living creatures within 100'. These must succeed in a DC 15 Will save or take 1d3 points of temporary damage to both Intelligence and Personality. On a natural "1", one of these points is permanent (player may choose which).
Brain-Bats are extremely intelligent. They can use corpses to speak when riding on one, and use both the living and the dead to further their schemes.