1. Personally, I think that the end and enderman is a great intro into a vast realm of possibility. I would like to see more creatures from the end spilling out into the minecraft world through mini-gates at random spots on the map. Perhaps mobs that use hi-tech (alien) weapons that are only slightly effective in the minecraft world, but in the end are really powerful.
2. I would also like to see mobs with weak-points and invulnerable points. Like skeletons or zombie pigmen with shields.
3. Ocean Monsters. Think Leviathan. Something like a gigantic sea snake.
I've always thought Sharks in only ocean biomes would be cool , but that they'll only attack you at half health and lower. Cause if you'd been attacked recently you'd be bleeding technically. (or a while ago if you have no food to get hunger bar healing you)
id like to see more villager usability as they are still useless , for example you build friendship points by trading with then maybe , once your 'friendship' is high enough they could defend you from other mobs and could maybe follow you into the neather / end to help you.
A griffon that can be tamed with a golden saddle (gold around a saddle)
Wild: 20 hearts
Will attack you if you aren't holding a golden saddle or beef
2.5 hearts a hit
Can fly 3 blocks high
Drops feathers leather and gold nuggets and very rarely a weak golden apple.
Tame: 25 hearts
You can mount it
Can fly 5 blocks high
Good control, will not run around randomly unless ordered
About as fast as a pig on ground
Ghast speed in air
Only drops feathers and a golden saddle when killed