I've just added a "BodyMonster" set to the HeroMachine 3 Alpha. These are actually just replacements for the legs, as you can see:
Holler if there's something you had hoped for but don't see. This does include the set of updated Monster bits from HM2, with the centaur(s), tree trunk, spider, faun, etc. I also included some requests from the Aliens thread with the ghost bottom, twister bottom, etc. I also cheated a bit and stole some elements from Insignia and Companions to make more half-human, half-animal hybrids possible beyond just centaurs.
Hope you like 'em.
