Super Mario Bros:

YSAOPE+YEAOZA+YEAPYA - Start on Final World

OZTLLX+AATLGZ+SZLIVO - Always stay big

SXIOPO - Infinite lives for both players

APZLGK - Super jump

APZLGG - Mega-jump

YAZULG - Moon Gravity

Hold A and press Start after a game over to continue where you left off

Donkey Kong:

SXNGOZVG - Infinite lives

PENKNPLE - Start with 9 lives

Godzilla:

Enter DESTR0Y ALL M0NSTERS as a password to fight all bosses on the hex board. REMEMBER: Use the number 0, not the letter O.

Contra:

UpX2, DownX2, Left, Right, Left, Right, B, A, and Start on the title screen for 30 lives per continue