Squirrel King

To get 99 continues, when at the continue screen countdown, press and hold B + C + Down + Start.

Hold B + C + Down + Start during the countdown at the "Continue" screen.

Reset the game and press and hold A + C + Right. At the bottom left of the screen, a 01 should appear, press C to increase the level. Press A + B + Up + Start to view the ending, or at the character select screen, press B + C + Left + Start for infinite health.