On any of the platform levels, press Start to pause the game, then press Up, Right, A, B, A, Down. Unpause the game to complete the sequence. With that code in place, pause the game again. To skip to the next level, press B. To access a cheat menu - with invinciblity, multiplier, and stage-select options - press C. With the code in place, you can use thses cheats on any stage, not just platform levels