These are Nether Mobs that you don't want to come close too.

1. Enderman - can teleport, they are creepy; do not look at thier eyes
2. Pigman - you can trade with them with gold. Make sure to wear some gold armour
3. Strider - ride them with a saddle and fungus on a stick.
4. Magma Cube - look like slimes but red. Cannot die from lava and they can jump on you and kill you.
5. Zombie Pigman - do not hit them as they will all come after you.