2-Player Level Select/Music Select  Player one determines level, second determines music.  Press the following buttons for the following levels: 

Press	For
Up+QP	Wolf Castle
Down+QK	Bridge
Up+QK	Stonehenge
Down+QK	Dojo
Up+MP	Jungle
Down+MP	Dungeon
Up+MK	Museum
Down+MK	Spinal Ship
Up+FP	Space Ship
Down+FP	Street
Up+FK	Helipad
Down+Z	Sky Stage

All Options  Press Z, B, A, L, A, Z during the story intro.

All Uniform Colors  Press Z, B, A, Z, A, L.

Change Colors  When selecting your character keep pressing Up or Down.

Credits  Press Z, L, A, Z, A, R during Story Mode.

Gold Fighter  Beat Training Mode on Normal with all A's.  

Master Difficulty  Beat the game on Extra Hard, or enter the All Options code at the intro. (Thanks to Jagr685062@aol.com)

Play as Gargos  Press Z, A, R, Z, A, B during the story intro.

Random Character Select  Press and hold Up and press Start.

Shadow Fighter  Defeat the Training Mode on Hard with all A's and an average of Grand Master.

White Fighter  Beat Training Mode with all A's on Easy.

Note:  White, Gold, and Shadow tricks only work for the fighter you do the trick with, and you must switch to the proper color to get it.