Get double ships on the Galaga Intro
Defeat the first wave of enemies in the Galaga intro in under 18.5 seconds and you will be rewarded with double ships on the next wave!

Saving Bosses to Memory Card
Any time you beat the game with a character, their boss will become playable. This can be saved to a memory card for future use.

Play a the last boss (Devil Kazuya)
Get a perfect score on all the Galaga games all the way through the game, and you will be able to play as the final boss. you cannot use the Double ship code, and you cannot restart a stage more than once. Then highlight Kazuya in Arcade Mode and press Start.

Play as the fake last boss, Heihachi
Play through the entire game without continuing.