Hudson's Adventure Island series stars a real-life Hudson executive called Takahashi Meijin, who is known as "16shot" for his famous ability to push buttons 16 times a second. In the game, he's a chubby kid in a grass skirt who finds weapons and stuff in enormous eggs. Just like in real life. (The game made a little more sense when it was called Wonder Boy and starred someone who didn't have a real job). What is it with Hudson and putting real people in their games?
Takahashi Meijin may be able to jam on some buttons, but you can influence his fake life with cheat codes. Advantage: you.
Adventure Island (NES):
Continue: Close to the "G" sign at the end of stage 1, jump up and down to make an egg appear, which contains the Hudson Bee. You can then continue your game by holding any direction and pressing start.
New Adventure Island (TG16):
Level Select: New Adventure Island is only new now in comparison with the original NES game. Given that it came out in 1992, it's a pretty Old Adventure Island itself. Press left, left, I, right, right, II, up, down, up, down at the title screen to select levels in this (much better, actually) semi-remake.