Mr. Do! Cheats

On some revisions of Mr. Do! (the Taito version for sure), there's a trick that will give you 255 lives in Level 1. This will only work if an apple appears in the first two rows of the playing field. Start by digging a tunnel from the bottom of the screen to right below the apple, leaving one thin layer of dirt to make sure the apple doesn't fall. Now kill all but one of the enemies in the level, then proceed to lose all your extra lives. On your last life, wait underneath the apple until the final enemy comes towards you. Dig the dirt underneath the apple causing it to drop, but shoot and kill the enemy as the apple drops before it squashes you. If everything's done correctly, the music will be messed up for a second or two and you'll be at the bottom of the screen, having been awarded 255 extra lives. Note that if you try to earn more than 255 lives, the counter will roll over to 0 lives.