Sega Master System / Mark III / Game Gear
When the "Start" and "Configure" options appear at the title screen, press before the Alien 3 logo fades out.
Start game play in two player mode and obtain a high score for both players. Intentionally have one of the players lose all their lives and enter
ALIEN as a name on the high score screen. The corresponding player will have unlimited lives when game play continues.
Enter the configuration screen. Enter two players and then start the game. Complete level one with player one and let player two die three times on the fans, now complete level 2 with player one. Player two will now start again on level one but will be graced with infinite continues.
See the main page for Alien³