Released: 1994, Super Nintendo
Final Fantasy VI is the sixth game in the long-running Final Fantasy series, and is considered by many to be among the best. It's earned quite a reputation online, as well, for being extremely prone to glitches, some of which actually render things unused that otherwise should be accessible.
But not even glitches can account for everything that went unused in this game: Enemies, spells, key items, dialogue aplenty, Esper effects, and even bits of code to modify the prices in shops all got left out. Did you know that it's actually possible to add the main villain, Kefka, to the team? This game is loaded with mysteries.