Well, naturally one thinks of Zelda when it comes to Classic (and some of the baddies are obviously inspired by some of the enemies in LttP).
Anyway, I wouldn't mind seeing skeletons of some kind. Maybe in some new section of Deadwood (Deadwood does need some love since more than half of it was removed). Maybe they just fall apart if you hit them with your sword, and then get back up in a few seconds. You'd have to kill them with bombs. Maybe 3 blasts to kill them. They should have a melee attack as well as a "bone boomerang" of sorts. Might be nice to have a baddy that you have to kill with bombs and is essentially immune to sword attacks.