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.
Information in this section was contributed by DJ Anca Peter.

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.
Information in this section was contributed by John Barret.

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.
Information in this section was contributed by Mad Conservative Crimefighter.