Enclave
God Mode & Complete mission options:
Pause the game, then press X, Y, X, X, Y, Y, X, Y, X, X, Y, Y.
Unlock the Dark Campaign:
At the episode selections screen, press X, Y, Y, X, X, Y, X, Y.
Fetica:
Get all the gold in the Dark Campaign to unlock Fetica as a playable character.
Stone Gnome:
Successfully complete the Dark Campaign to unlock the Stone Gnome as a playable character.