Black Brimstone

In order to unlock Black Brimstone, you need to beat the Boss Attack game in multiplayer mode 20 times. THEN you highlight Brimstone on the character menu and press Left and Right triggers, plus the A button simultaneously. You will see Black Brimstone appear in the character select box. This is the only method that worked for me.

All Characters

Another way of unlocking Spawn I is by playing Gatekeeper (player 1) and Brimstone (CPU) on the highest difficulty setting. This is the only way I've been able to unlock this character. The method already posted here did not work for me. The method I found also opened more levels and bosses to fight (Angel Teneres and Dark Ages Spawn) that were not part of the normal Boss line-up.

Secret Characters

Ok, this is what worked for me. Beat the Boss Attack mode without ever continuing on multiplayer and the characters will unlock as follows. One Time: Spawn I Five Times: Dark Ages Spawn Ten Times: Spawn IV Fourteen Times: Admonisher

All Characters

Play as these characters with the level settings on level 4 in Arcade mode on one 
player with no CPU ally

Play As		To get

Clown		Vindicator
Tiffany		Angels E
Spawn		The Curse
Sam		The Mafia
Twitch		Soldier 1
Brimstone		Overtkill
Grace		Soleil
Tremor		Cy-gor
Coglostro		Vandalizer
Jessica		Green Beret A
Redeemer		Hell Spawn
Al Simmons		Skeleton 1
Vindicator		Vacillator
The Curse		Curse Sub
Overtkill		Army A
Angel		Teneres
Soleil		Wolf 1
Vandalizer		Vaporizer
Hell Spawn		Gatekeeper
Gatekeeper		Zombie 1

To get the other characters play on level 4 with a CPU friend (note: the first 
character listed is the character you need to be)

Spawn & Gatekeeper	Spawn 1
Spawn 1 & Al Simmons	Dark Ages Spawn

Spawn with Cape

With spawn during gameplay, press A, X, and B all at the same time. Spawn will have a cape momentarily. He will be much stronger.

Secret Photos!

Choose tournament mode and select any character, beat the game and you will unlock secret pictures of your character. To view the pictures just go to the "gallery".

Transformations Update

To transform into better fighters(eg.Spawn) you don't have to press R+B. By pressing X+A+B at the same time will work too. Spawn's Transformation: He get's a cape and his abilities are increased. He can jump higher (really high) and his attacks are stronger. Spawn's Trans. does not use up his life but it starts to dissapear after 10 seconds. Note: Only Caped Spawn can use his Chain's in mid-air. Clown's Transfomation He transforms into (of course) Violater, he can shoot fire from his mouth (chargable), Through Glowing balls,and some other attack i cant remember. Note:As Violater Clown's Life Meter drains very fast. Brimstone's Transfomation Brimstone turns in Dark Brimstone.His attacks are real strong and he looks cool. Also his fireball Attack is stronger than as Brimstone.(incase you dont know his fire attack use Fist attack and press and hold the R button.Note: Dark Brimstone has a Self- Destruct attack that hurts everyone that's near him.It drains all your life but does not kill you.(I use it as a last resort but it takes time to use it just press and hold R) Sam's Transfomation Sam get's real pissed-off you can trigger it only your attacker can when you are knocked down press X+A+B and he'll get up and turn red you can also see smoke above his head. In case you dont know this Same can heal himself. Just switch to Fists and press R Sam will then eat a piece of pizza that heals him a bit.

Transform into the Massives!

This code requires a unique amount of health (mostly half health to the full amount). Take the following characters and press R trigger + B to transform the character. (NOTE: The character will lose health the longer he is transformed so press R+B again to change them back to regular form). Characters Forms Clown Violater Spawn(All of them) (Add on)Cape Brimstone Dark Brimstone Sam Get's pissed off (very powerful) Some secret Characters may change as well but I'm not aware yet. Have fun and shock your friends.