Finish the game on Normal difficulty.
Finish the game on Hard difficulty.
Finish Time Attack mode multiple times to unlock new characters or donate gems in story mode to the laboratory.

Successfully complete the game under the super hard difficulty setting.

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.