The Grim Adventures of Billy & Mandy Cheats for GameCube

Unlock Dracula:
Beat Mission 5 Tier 3 in mission mode.
Unlock Jack the Pumpkin:
Beat Mission 9 Tier 2 in mission mode.

15 of the 2nd set character costumes become available when you have completed ALL the Mission mode matches.

Using any Character complete Story mode to unlock an outfit for them.

You can play the first 4 unlockable characters in 'VS. Mode' but you have to unlock them in 'Story Mode'.
Unlock Eris:
Using either Billy, Mandy, Grim or Irwin beat 'Story Mode' once.
Unlock Fred Fredburger:
Using either Billy, Mandy, Grim or Irwin beat 'Story Mode' once.
Unlock Mogar:
Using either Billy, Mandy, Grim or Irwin beat 'Story Mode' once.
Unlock Nergal:
Using either Billy, Mandy, Grim or Irwin Beat 'Story Mode' once.
Unlock Hoss Delgado:
In Tier 1 in 'Mission Mode' beat Mission 9.
Unlockable Horde Characters
Complete the following tasks to unlock the corresponding effect.
Unlock Vikings:
Using ALL the characters beat 'Story Mode'.
Unlock Chicken:
Using ALL the characters on any difficulty with 10 hours of gameplay beat 'Story Mode'.
Unlock Nerglings:
Using ALL characters on any difficulty beat 'Story Mode'.