Damn, playing on Hard mode is so fun (and hard, of course.)
I've been playing the "delete-world-if-you-die" thing and it really gets interesting at night.
There's swarms of creepers (one creeper is the "leader," all others in the group follow. If the leader hisses and swells to explode, so do the others. The leader moves 25% faster than the player on Hard.)
There's werewolves, which are extremely resistant to all but a gold sword
There's giant creepers, which are extremely slow but make a massive explosion.
There's the usual assortment of bad guys, also including mummies, black souls, wolves, wraiths, ogres...
Right now I just died after being attacked by a desert lizard. It was either take the long way through the sandbar and a single desert lizard, or swim through the water with two sharks.