You can get rid of the baddies by making them fall from ledges in the game. It works especially well at the end of level II. Go as far as the screen will allow, then walk backwards, and fall down from the raised area. You will back down onto the platform below. Move down alongside the platform edge as far as you can and all the baddies will fall down.

Start a two player game, then press both fire buttons and the 'ESC' key. You will now have unlimited lives. On the title screen press 'ESC' then type: "YEP, I CHANGED THE CHEAT MODE ON THIS VERSION". Now press 'RETURN'. Start the game and you will be playing upside down.