X-Men - Next Dimension cheats and cheat codes for Gamecube

Cheat mode - Unlock everything:
Hit Up, Up, Down, Down, Left, Right, Left, Right, A, B, Start, Start 
at the main menu.

Single-hit kills:
Hit Up, Up, Down, Down, X, Y, Y, X at the main menu. 
Re-enter the cheat code for slow deaths. 

Unlimited supers:
Hit Up, Up, Down, Down, A, X, A, X  at the main menu.

Toggle AI:
Hit Up, Up, Down, Down, A, A, B, B, X, X, Y, Y at the main menu.


3rd outfit
Finish story mode with any character

4th outfit
Beat 20 matches in survival mode with any character

5th outfit
Finish arcade mode in hard mode with any character

6th outfit
Beat all 10 fighters in time attack mode less than 15 minutes

Unlock Bishop
Finish arcade mode with Gambit

Unlock Blob
Finish arcade mode with Bishop

Unlock Dark Phoenix
Finish arcade mode with Phoenix

Unlock Psylocke
Finish arcade mode with Betsy

Unlock Sentinel A
Finish arcade mode with Cyclops 

Unlock Sentinel B
Win twenty matches in survival mode

Unlock Bastion
Finish story mode with Magneto without losing a single matches, then 
defeat Bastion


Endings:
There are 3 possible endings in story mode:

Regular ending: Beat Bastion with Magneto.

Alternate ending: If you lose the Magneto vs. Bastion fight, you can fight
with Phonix against Bastion. Beat Bastion with Phoenix.

Secret Ending: Reach "Perfect" victory in the Phoenix vs. Bastion battle.
This will also unlock Dark Phoenix also.