Battlemaniacs

A licensed port of Battletoads in Battlemaniacs with an interesting backstory which eventually led the game to be released only in Brazil (and in an unfinished state, at that).

Level Select#

In the short period before the opening text appears, press Up, Down, Up, Down, Left, Right and listen for a sound. Alternately, set RAM value 757 to anything other than 00. Start the game afterward for the Level Select.

Note, there's a 94 frame (about 1.88 seconds) delay after resetting or booting the game before the code can be input, then the player only has 60 frames (1.2 seconds) to punch it in.