Unlock better variety of mini-games: play as Cartman because he is the only character that can play the Rodeo and Beefcake mini-games.
Win Spank The Monkey mini-game: the monkey's butts become redder every time Mr. Mackey hits them. Try to watch the order that the butts turn back to normal.
Beefcake bonus: eat every single can of Weight Gain 4000 in the Beefcake mini-game to unlock a bonus animation at the end.