Unlockable Features:
Time Attack Mode - Finish the game on Normal difficulty.

New Characters (Monsters and Allies) - Finish Time Attack mode multiple times to unlock new characters or donate gems in story mode to the laboratory.

Endless Mode - Finish the game on Hard difficulty.

Alternate Title Screen:
Beat the game on Super Hard difficulty.

Unlockable Maps:
Vs. & Training maps 10-16 - Beat Super Hard difficulty.

Easy EXP Crystals:
Get up to Stage 3-16 (the place where you only encounter 2 knights on a long metal bridge) And keep fighting the 2 knights, but staying at the left screen. Get any EXP Crystal they drop, and go back to the left agian. You can get up to 99999 quickly.

Unlimited "Invincible Body" Time:
When you die, the end boss shows up and says something like "If you sell me your soul, I'll give you an invincable body for a while. what do you say?" Say yes and while your soul is being sucked up by the big blue beam, press ALL the buttons on your gameboy randomly. The glitch only works if you are only pressing the buttons while your soul is being sucked up. Afterwards you should see your time says 999 and never goes down.