Adam Sandler:
Enter Adam Sandler as a name in Make A Character mode.

Cousin Grimm:
Successfully complete Episode 1 with a "Perfect" rank.

Frankenstein:
Successfully complete Episode 2 with a "Perfect" rank.

Mummy:
Successfully complete Episode 3 with a "Perfect" rank.

Tomb ring:
Successfully complete Episode 3 with a "Perfect" rank.

Wolfman:
Successfully complete Episode 4 with a "Perfect" rank.

Graveyard ring:
Successfully complete Episode 4 with a "Perfect" rank.

Alien:
Successfully complete Episode 5 with a "Perfect" rank.

Spaceship ring:
Successfully complete Episode 5 with a "Perfect" rank.

Gladiator Nick Dimond:
Successfully complete Episode 6 with a "Perfect" rank.

Wizard Johnny Gomez:
Successfully complete Episode 6 with a "Perfect" rank.

Alternate fatalities:
When certain conditions are met, each fighter can perform an alternate fatality.

Head Rip: Kill your opponent when they have lost both their legs. 
Anvil Drop: Kill your opponent when your fighter has lost both their legs. 
Matrix Decapitation Kick: Kill your opponent when your fighter has lost both their 
arms. 

Cut off the celebrity's arms or legs to do an alternate death kill. For example, 
Carmen Electria has saws. Keep hitting the other celebrity with the saws and either 
the arms or legs will fall off. Note: Once you take off a celebrity's arms or legs, 
they use an attack that throws them at you. Although it does not take off too much 
damage, you will not be able to block the attack. 

Easy wins:
Play as Dennis Rodman. When the fight starts, get close to the opponent and keep 
pressing Y. The basketball should keep on hitting the opponent on the head for an 
easy win.