Character galleries:-  Successfully complete a tournament battle with each character to unlock the corresponding gallery. 

Hidden characters:-  Successfully complete Boss mode to unlock various hidden characters.

Play two-player in Boss-attack mode. If you successfully complete the game, even more characters will be awarded.

Powered-up characters:-  Make sure your character has almost full health, then press R + B or X + A + B. Most characters have an alternate powered-up form. However, the powered-up version will gradually drain your remaining health. Press R + B or X + A + B again to return to normal form. 

Cogliostro's magic:-  While playing as Cogliostro, hold R button to form a floating green pyramid. Anyone can step into it and regain health, which only lasts for a short time. Also, press R when Cogliostro hands are green or blue to increase the distance and strength. 

Grim Forest: Hidden areas:-  On the Grim Forest level, run through the red lit parts of the trees to get to hidden areas. 

Get rare items in Boss mode:-  Use this trick to get the rare items in the Item Collection Gallery, which will help unlock more secrets. Play in team mode and successfully defeat every opponent within the time limit. If you get to the Gate Keeper and defeat him within the time limit you will fight two extra characters: Angel Teneres and Medeival (Dark Ages) Spawn. You will find your character's ultimate items on the levels that you fight them on, assuming that you are playing at level 4 difficulty or higher. Examples of rare items are: Bikini of Steel special item, Stinger Missile Launcher, Clown's Gun, etc.

Admonisher's secret room:-  If you face Admonisher in the smelting pit, there are many booby-trapped doors. However, one is not trapped and holds a secret storeroom. You will find Sword of Curse 1 in there, among other goodies.

Extra Boss in Boss mode:-  While fighting Vacillator on the stage with water (not ice), go all the way to the other end from where you start. Blast the wall with anything and go inside to find Vandilliser. He will not have as much life, but he will be as hard of an  opponent. 

Play as Black Brimstone:-  Successfully complete the game in Boss mode with every character and also unlock all hidden characters. You do not have to complete tournament mode. Highlight Brimstone in any mode, then hold L, hold R, and press A while holding both of those buttons.