I think their should be more animals in Minecraft such as reindeer.
Also, i think that the reindeer should poop rainbows. just kidding.
Actually i think the reindeer should be tame-able, attack players or animals that attack it, and eat sugarcane.

Alright now about the elemental creatures.
I think their should be fire slime cubes in certain areas of the Nether and red colored skeleton mini bosses in the nether that shoot fireballs out of their mouth.

This is it now, goodbye.