
The "evil clown" thing probably got its start in the 80s, from Pennywise the Clown in Stephen King's It. I'm pretty sure that came from either King remembering some loud, scary clowns in his childhood or his kids being frightened by clowns. Garfield and the Simpsons had their own obnoxious clowns as well (Binky the Clown and Krusty the Clown, respectively.)
A lot of "indies" seem to be thinly veiled "homages" (to be nice about it) to well-known games. Eastasiasoft seems to really try to push the limits of what the new, more tolerant Nintendo will accept as far as nudity. We've come a long way since Mortal Kombat on SNES.