The obstacle in making Bats villagers is actually making them likeable. Bats are pretty ugly animals, they look like monstrous mice with wings (actually, the French word for bat is chauve-souris which means bald-mouse). If the Nintendo artist can make likeable bats, than we are good to go. But, right off the bat like that, I don't think we are going to get bats, worms or snakes villagers...