The Grim Adventures of Billy & Mandy Cheats - GameCube

Unlockable Characters
The first 4 unlockable characters can already be played in "VS. Mode". But you have to unlock them in "Story Mode":

Eris - Beat "Story Mode" once with either Billy, Mandy, Grim or Irwin
Fred Fredburger - Beat "Story Mode" once with either Billy, Mandy, Grim or Irwin
Hoss Delgado - Beat Mission 9 in Tier 1 in "Mission Mode"
Mogar - Beat "Story Mode" once with either Billy, Mandy, Grim or Irwin
Nergal - Beat "Story Mode" once with either Billy, Mandy, Grim or Irwin
Lord Pain - Complete Mission 9 in Tier 5
Nerglings - Beat Story Mode with all characters on any difficulty
Vikings - Beat Story Mode with all characters and destroy every letter in the credits

1st Set Costumes
Complete the Story mode with any character to unlock an outfit for them.

Unlock Characters
The first 4 unlockable characters can already be played in "VS. Mode". But you have to unlock them in "Story Mode".