The game files contain data for an unused weapon called "The Killer Bow".
Contributed by MeleeWaluigi
The Moogle was initially created for Final Fantasy II as a race called クライオ (Kuraion, lit. "Clion") that lived in cold regions, but they were scrapped along with several other races. Their sprite and race details became the Beaver race in the finished game.
Contributed by Cavery210
Final Fantasy 2 was planned to be released to the USA around 1991 as "Final Fantasy 2: Dark Shadows over Palakia". The game was ultimately never localized due to the approaching release of the SNES.
Contributed by Cavery210
Many spells in the original NES version are bugged:
Aura does nothing at level 8.
Barrier does not grant protection against ice at level 8.
Dispel doesn't work at all.
Protect only works on the caster.
Sap won't work on enemies with more than 256 MP.
The Ultima spell was supposed to increase in power relative to the level of all of the other spells the caster has but won't even if all other learned spells are at level 16. This means that Ultima will only do about 500 damage at level 16.
Contributed by Shinitenshi
When a party member dual wields two weapons, even though there is an animation of the weapon being used, the game only calculates damage based on the first weapon. This is fixed in later versions.
Contributed by Shinitenshi