Juuryoku Soukou Metal Storm
Metal Storm is an NES game by Irem where you basically play as Captain Viridian's mecha ancestor.
The Game Genie code YASNUKZA enables a level and powerup select. Press Up and Down to select a level, or Left and Right to select a powerup (the five sets of letters will change depending on what powerup you select). The powerups, from left to right, are None, Shield, Gravity Fireball, Armor, and Power Beam. Press Start to enter the selected level.
The Japanese version of Metal Storm contained a neat little intro sequence, which was disabled in the US version. However, the code was left mostly intact, and can be re-enabled using the Game Genie codes SNKEPULO and OOKEZLVP. The only things removed were a "TAMTEX" logo (the division of Irem that developed the game), a few screens of Japanese text, and the tiles for an exploding planet animation, which suggests that Irem originally planned to keep the intro. Why it was ultimately disabled is anyone's guess.
The Tamtex copyright was also removed from the US title screen, leaving only the Irem copyright.
In the Japanese version, the last boss says "You will die with me..." after you defeat him. Also, the epilogue, while still in English, is completely different from the one in the USA version. Finally, the credits list in the Japanese version has one name that was very strangely removed in the USA version: Hiroshi Futami (Producer).