Kreeps:A form of ghast that eats Zombie Pigmen. There a little weaker then there brothers and wont attack you unless you hit them first. You will normaly see 1 (for every 3 ghast theres 1 kreeper) . They will attack pigmen on sight so if seen stay away from pig men. The only true threat is there scream that when being attacked they scream and all Ghast around focus on the attacker. (they fight pigmen with Snowballs that injure the pigmen but not you). Pigmen killed by them will not drop any items.

Jaws:A red Shark like creature that attacks you while swimming.  There only found in deep water so dont worry it your in a pool or hottub. They drop teeth which can made stronger arrows.

Boar: A brown furry pig that attacks. They are always in groups a 3 and wont stop to attack. Weak but scary. Can you dig it.

Goblin:A Neutral mob that can passively travel threw the Nether (not threw your portal threw there own. There portals are small stones left out in the world that help travel. In the nether they work like miners (they wont be mining but there basically the nethers tortured miners.)  There only going to be in the desert biome so dont worry for in conveyance.  after killing them you can brake the stone so they wont spawn there again. (they spawn in the desert because they like it hot