At the options menu, press A, C, A, C, A, C, A, C, B(x4). If done correctly, you'll be taken to a screen where a message and a smiley face of David Perry will appear (the co-developer of Virgin Games), and you'll hear Aladdin say "Yeah!" A cheat menu will appear, giving you access to such options as invincibility, level select, and more.
More Cheats, Achievements
