Rush'n Attack

Run in midair

Press B while standing, then press Up while the knife is pulled out.

Crouching knife in air

Hold Down, then quickly press B (while still crouching), then quickly press Up.

Music in demonstration mode

Hold A + B +Select + Start and turn on the NES. Release the game after it returns to the title screen. When the demo begins, it will have music and other sounds.

Hint: Continue where you left off after losing a life

Unlike in a single player game where if you lose a life you must restart from a predetermined point in the level, in a two player game you will restart from the same point with a few seconds of invincibility. Simply start a two player game and have the second player intentionally lose all their lives. Your game and Boss battles will become a bit easier.