Mask:
Enter arcade mode. When the best record appears, press Right, Left, Right, Left, X + Y. Mask should be now be unlocked. Alternately, clear legend mode with all hidden characters.

Additional fighters:
1. Robbie Lawler
2. Tsuyoshi Kosaka
3. Vitor Belfort
4. Pat Miletich
5. John Lewis
6. Dan Severn
7. Jeremy Horn
8. Hayato Sakurai
9. Maurice Smith
10. Mark Coleman
11. Mikey Burnett
12. Bas Rutten
13. Gary Goodridge
14. Frank Shamrock
15. Marco Ruas

Big John McCarthy:
Unlock all regular fighters, then win all Silver belts in championship mode with all of them.

Bruce Buffer:
Win 33 consecutive matches in arcade mode.

Frank Fertitta:
Lose 66 bouts in arcade mode.

Larry Landless:
Unlock all regular fighters, then win all Silver belt in championship mode with all but one of them.

Skyscrape:
Clear legend mode with all normal characters.