Slogs: Hate them, and so do you! To kill them, use the code 1817 to get their weakness, a gun

Guinea pigs from heck: Fast, not so fluffy, and dangerous. Kill 'em any way you like!
Tentacle-faces: You only face them once, and you don't end up living. It is fun to see one of them decapitate.

Sirens: You can tell these because of their distinct voices. Kill them anyway you like.

Kenny!: OMG you killed Kenny, or at least you will when you get exploding arrows and a crossbow.

Crawlers: Smash them! It's like playing Whack-A-Mole.

Crawler Hive: Kill him any way you like, but make it snappy.