Salmon-Pink Max

You can destroy the enemy biplane by flying through the edge of the screen and firing horizontally, then immediately turn around and fly back through the screen to the other side. Line up and fly through your own bullet and the opposition will explode!

This cheat works due to a bug by the programmer. He detected a kill by seeing if a bullet from a player had hit any plane, rather than checking which plane was hit! The cheat also works in the original, Biplane Duel.

(Source: Lemon Amiga)