I hope we have some kind of necromancer or summoner enemies. Those always are interesting, even if a bit annoying en masse.
I like the idea of the lumbering enemy that charges you and keeps going if he misses.
I also think a turtle enemy that pulls in to his shell and becomes a physics object could be fun to play with. (And yay, mario reference.)
Basically, I want some classic monsters, and some off the wall unique monsters that utilize the physics, lore, or art direction. From a top-down view with big heads, a monster where the head and body split and attack separately could be a good surprise. A monster that does little to no damage, but bounces you around or grapples on to you and slows you down. Murk creatures and clockwork room changers. All that fun stuff.