Batman Forever (SNES)
This game has a hidden level select.
A mediocre Mortal Kombat-esque beat 'em up with awkward controls. Too bad you can't do fatalities.
On the main menu, press Left, Up, Left, Left, A, B, Y (LULLABY). The screen will flash to indicate success. Change the game type to Normal Game and choose your character to bring up the level select screen. Pressing Up or Down will toggle the stage, and Left or Right will toggle the level. In a level, pressing Start, L, R will inflict damage on all enemies on screen.