The Shaman-thief starts off with the cheese. All mice must chase the shaman, and the first ten Mice to touch the shaman get the cheese. After all the cheese has been taken from the shaman, he is killed.
The golden name text on a selected mouse is listed as the Shaman-thief for the map. Keep in mind, though, that maps such as this one, where the thief steals the cheese, will not reset your points and you are very likely to be a normal shaman soon after. The shaman-thief can't do much other than stall. The shaman-thief can block off the mice, jump to the very bottom and walljump stall at the bottom of a plank (very frustrating for most walljumpers), fly using skills, spirit, or balloon, or die.