Monster Force Stage Skip
During gameplay (but not while pausing), hold L, R, and A, and then press Up to complete the current stage.
Monster Force Become Invincible
When the game is paused, hold L, R, and B, and then press Down. You should hear a sound. Now your life should be automatically refilled.
Monster Force Exit Stage
When the game is paused, press L, R, and A together to return to the stage select screen.
Monster Force Play as Drew or Mina
On the character selection screen, hold L, R, B, and Right together.