Carrion Carcass Get a bronze or better on the Rare
Corporal Hart Complete story mode on the normal or hard difficulty
Dr. Peabody Complete the Amateur League with golds
Zombie Monkey Complete the Behind The Undead challenge with a medal
Human sounds Complete the Cats Out Of The Bag challenge with a medal
Play music You can play some music in arcade mode... Firstly you need to pick a game type... Any one will do except for mapmaking. Then select Disco and a character. Then move over to the instruments and press some buttons.