Unlock Testament
Defeat Testament when he challenges you in stage 9.

Unlock Dizzy
Defeat Dizzy when she challenges you in stage 10.

Original mode
Successfully complete the game in survival mode to unlock the "Original Mode" selection at the options screen.

Extra mode
Defeat a fighter's dare devil version in survival mode to unlock extra mode for that fighter. The fighter's extra version is able to execute new moves and supers.

Fight as Dizzy or Testament
Press Down, Right(2), Up, Start at the "Press Start" screen.

Alternate costumes
Press Start or Select when choosing a fighter at the character selection screen.

Guilty Gear mode
Select survival mode. Get to stage 180, then continue on and defeat all opponents until reaching stage 330. The Guilty Gear versions will now be unlocked.