Press A + X when operating your character to advance to the next level and become invincible. Note that the earning of achievements will become disabled while cheat mode is activated.

ACHIEVEMENT - HOW TO UNLOCK
2x Multiplier - Get a 2x multiplier.
4x Multiplier - Get a 4x multiplier.
Adventure Mode Completed - Beat level 89 in Adventure mode.
Black Belt Grandmaster - Beat all levels in Adventure mode on the Black Belt difficulty.
Tally Mode Completed - Beat level 89 in Tally mode.
Black Belt - Reach the Black Belt difficulty.
Blue Belt - Reach the Blue Belt difficulty.
Brown Belt - Reach the Brown Belt difficulty.
Green Belt - Reach the Green Belt difficulty.
Orange Belt - Reach the Orange Belt difficulty.
Purple Belt - Reach the Purple Belt difficulty.
Yellow Belt - Reach the Yellow Belt difficulty.