The final boss, Zeromus, had a complete redesign for Final Fantasy 4 Easy Type. He was also made a lot harder, such as using Big Bang at the start of the battle. Zeromus EG in the Game Boy Advance and PlayStation Portable version is based on this version.

In the Japanese version each character had multiple abilities, some of these abilities were cut in the American version and the Easy Type versions for being less useful in battle than other abilities.

In the final battle against Zeromus, Edge can steal an item known as Dark Matter in the Japanese version of Final Fantasy 4. This item, long thought to reduce the damage of Zeromus's Big Bang attack, is actually a joke item. In the DS version, a superboss named Proto-Babil appears if you use this item on the face of the Moon.

In the version 1.0 release of the game (which only exists in Japanese), there was a bug that occurred when exiting certain areas of the game that messed with the game's RAM address of which location the player was in. Due to this, when exiting certain dungeons and then flying to the underworld, the game would think you were inside a lunar dungeon and read from the wrong set of enemy AI tables when entering battles. Due to this, enemies will spend the entirety of the battle using Stone on themselves and their teammates until all of them are defeated. The only difference between versions 1.0 and 1.1 is a bugfix for this.