On the high score table or wile playing, enter "NANCY" for your name. This will give you infinite lives. Press 'RETURN' to skip levels.
Play a game, get into the high score table, enter your name, then play another game. Press Fire so you can move about, find a safe place where you could stand still for a while and not get killed, then stand still a while and type in "DISCOVERYSOFTWARE" and press 'RETURN'. You should see a message on screen. You will now have infinite lives and will go to the next level. Now you can press 'RETURN' anytime to travel to the next level.
Alternatively, If you type "RAD" into the highscore table and play another game, you will have unlimited lives!
Select your player, start the game, and kill yourself off. Then play again with the same character, and while the game loads keep hitting 'Return'. This should also give you unlimited lives.
Once loaded, select the HERO, then lose all lives on the first screen. Now select the HEROINE, and you should have infinite players.