Codes:
During the vs. screen, press Down and Start at the same time. Easy Combo Breakers

Hold Right + L + X + Y on the Vs. Screen (Both controllers if 2-Players) Fast Speed

Hold Right + R + A + B on the Vs. Screen (Both controllers if 2-Players) Faster Speed

Hold Left + L + X + Y on the Vs. Screen (Both controllers if 2-Players) Fastest Speed

When selecting a character press: up or down. Get Alternate Costumes

Select Cinder. At the VS screen, hold right and press L, R, X, B, Y, A. Play as Eyedol

When you are selecting characters hold Up and press Start. Select Random Characters

Hold Left + R + A + B on the Vs. Screen (Both controllers if 2-Players) Slow Speed

Hold left then press b,a,b,a on the vs screen No Combo Breaker

Stage Select/Music Select:
On the character select screen, Hold U or D with the specific buttons as shown below. The button you press will also choose your character, so be sure the fighter you want is highlighted when you do the code. In two player mode, The first person to pick their character gets to choose the stage. The second player gets to pick the music according to the same button combinations used for the stage select.

U+L - Ice Temple
U+R - Castle Roof
U+X - Ice Sculpture
U+Y - Skull Room
U+A - Desert Roof
U+B - City Roof
D+L - Canyon Bridge
D+R - City Street
D+X - Lava Pit
D+Y - Bloody Arens
D+A - Factory
D+B - Fireplace

Come back to life:
In VS mode, when you run out of life and your opponent has the opportunity to finish you off, start hitting random buttons like crazy. There is no specific sequence. If you manage to hit the buttons fast enough before your opponent hits you again, you will come back to life with only a sliver of health, but your attack power will be enhanced greatly. If you get hit again, it's over.

Practice Against Eyedol:
Fight your way up to Eyedol, then let him kill you. At the game-over screen, let the timer run down and then go to "Practice", pick your character, then you'll be practicing against Eyedol.