yes creepers,skeletons, pig Zombies, ghasts, enderman, enderdragon, silverfish, spider, cave spider, spider jockeys, magma cubes, blazes and slimes
No, but enraged ones have red eyes which could possibly be mistaken for zombies.
no
Blue
There are no hostile mobs in Peaceful difficulty mode on Minecraft. Mobs such as creepers, skeletons, zombies, spiders and all other manner of hostile mobs do not spawn while Peaceful mode is active, though you will see (in dark places or at night) mobs attempting to spawn and immediately disappearing a millisecond after appearing. Mobs cannot attack you regardless unless another difficulty is triggered.
no
Skeletons can make any agressive mob fight. I've seen skeletons and zombies, creepers, spiders, other skeletons, and even endermen fight. I've even seen two spider jockies fighting.
Delete the .minecraft folder in your AppData folder and delete any shortcuts you have placed (on your desktop, in any other folders that you keep games).
Alligators have eyes like any other creature.
yes for example, if a bird eats a crab then the bird can be eaten by another animal, its like a foodchain
Minecraft started out as Cave Game, back then it was just an idea, minecraft just expanded not really copying any other games.
Strangely enough MAN - we are responsible for killing more things than any other creature.
As of scientists knowledge, no. There are currently no zombies, nor is there any evidence of any.