Spiders: Most Spiders come in the mountain in the night so don't stay there.

Skeletons:They like to hang around dark places in the night so if you're in a creepy stronghold then come with armor.

Witches:They are often found in villages with a cauldron. Hit one as soon as you see one. Witches can be tricky.

Enderman: They vanish instantly before your eyes. They are hard to hit.

Creepers:Run away as soon as you have got a creeper dead or they will explode and you will die.

Dark Creepers: They spawn in lava pools in the Nether (it is fire immune). They throw Dark TNT at the player. 

Ghasts: They are only found in the nether. They shoot fireballs.

 Nether Dragon: The Nether Dragon is a boss mob which can be found in the Nether. The Nether Dragon is a very deadly force of destruction.