Frantix
While on the level select screen hold down the L and R buttons. “Cheats” will appear and you’ll be given 8 spaces within to enter characters. Use left and right to move spaces and up/down to switch the character. The following codes will achieve the desired effects:
LVLANY0 – Acces any level OFF
LVLANY1 – Access any level ON
INVINC0 – Invincibility OFF
INVINC1 – Invinicibility ON