For tons of lives, follow these instructions: Set up a two player game. Player 1 must get an extra life. Now both players should lose all their lives. Player 2 will return with 99 lives, and when he loses one life, Player 1 will have 99 lives too.

Here are the passwords for those elusive later levels. To enter a password, press 'F1' (one player) or 'F2' (two players), select control by pressing 'Fire' on the joystick, and you'll be asked for a password.