Blooper: Before fighting the Unversed alongside Mickey in Radiant Garden, if you look carefully behind Aqua, you can see a second Kairi right behind her. This was rectified in HD 2.5 ReMIX version.
Executive Meddling: Two changes were made to a couple story endings because the producers thought the original plans ended on notes that were too depressing. The Final Episode was originally part of Aqua's story but split off into its own scenario, while the scene where Ven is absorbed into Sora's heart was given a framing scene with Sora and Riku on the beach.
The Reunited Ventus and Vanitas is sometimes called Venitas.
Before names were released, Master Xehanort was referred to as OBM (Old Bald Man; in the vein of BHK/Blond-Haired Kid for Roxas). When his name was released, we got affectionate nicknames such as Baldinort, Baldsem, Geezernort, Oldynort, and Grampinort.
There's the Captain Obvious-styled Evil Sora for Vanitas. The epilogue also gave birth to KH Jesus for Sora.
As well as Jesusora.
A less common one for Vanitas: Soranitas.
Red Eye for the unnamed Heartless that serves as the boss of the Secret Episode, later given the canon name Dark Hide.
Fan Translation: With the original Japanese PSP release of the Final Mix version of this game. Like KHII FM, BBS FM was translated to English, this time thanks to Key To Truth. You must patch the game itself in order to play it in English, which you can do with either an ISO (for Emulation) or with an actual game cartridge.
Sora's gonna save Terra, Aqua, and Ven from their fates.
On February 2009, a troper speculated the possible connection between the armor Xemnas wears in Kingdom Hearts II and the armor the protagonists wear. That armor is Xehanort's Keyblade Armor that he wore when he was younger.
Serendipity Writes the Plot: The secret endings of Kingdom Hearts II that tease this game show the three protagonists wearing armor with capes. The capes were intended to be in the final product from the start, but had to be removed because their animations caused FPS issues during multiplayer.
Bret Iwan replaces the late Wayne Allwine as Mickey. Surprisingly averted by Chris Sanders, who still reprised his role as Stitch despite now working forDreamWorks Animation, Disney's primary rival in animated films, following behind-the-scenes conflicts on Bolt.
In the Japanese version, Captain Hook is voiced by Naoya Uchida instead of Chikao Otsuka, presumably because the latter voice actor was also voicing Master Xehanort.
Averted in the case of Captain Hook due to The Other Darrin (Naoya Uchida, who in fact is the usual Other Darrin for the Japanese Hook); in the rest of the series and in the Japanese dub of Peter Pan, Hook is voiced by Chikao Ohtsuka. Ohtsuka's in this game, but is playing Master Xehanort. And even if Ohtsuka did voice Hook here, the pirate and Master Xehanort do not cross paths anyways.
Played straight in the English dub by David Ogden Stiers, who plays two of the seven dwarfs (Doc and Happy); Russi Taylor, who plays Minnie Mouse, Huey, Dewey, and Louie, as well as the Fairy Godmother and Drizella (though the two don't have any scenes together); and Jim Cummings, who plays Pooh and Tigger. And that's just naming the characters who share worlds together! The actors mentioned (and a few not mentioned) play other characters as well, though those characters aren't even in the same world as each other.
Nomura considered showing Leon and Cloud's past in the game. He decided against it because Radiant Garden was already showing the past of seven Organization XIII members, so including the Final Fantasy characters on top of them would have overloaded the world with too many characters.
A world based off of The Jungle Book world was going to be featured, but was pulled out. It was likely cut due to legal issues with the late Louie Prima's estate, as the character King Louie is a caricature of him.
Pleakley would've made an appearance in Deep Space.
The Blob Mob was originally a boss, but it was reworked into a normal enemy due to issues with how many bosses were in the game.
The "Birth by Sleep: Volume Two" secret ending of Final Mix hints at a sequel for the PS Vita, though it was axed because the producers thought that there were too many portable games in the franchise. Ideas from the proposed sequel are present in the 2.8 complitation.
The first trailer shown at Jump Festa 2008 had a lot of scenes that weren't in the final game, or took place differently. Those scenes include Terra thanking Ventus for saving him from an unspecified incident at the Maw of Hallow Bastion, Ventus talking to Xehanort at the Olympus Coliseum, Terra watching a young Sora and Riku sparring, Terra defending Ventus at the Maw instead of the Land of Departure, and Ventus requesting Terra and Aqua to erase him at the Destiny Islands instead of the Keyblade Graveyard. Most of these can be chalked up to the assets for the new worlds like Land of Departure not being done at the time of the trailer's release.
Another Titan from Hercules was considered to be added as a Bonus Boss in the Final Mix version instead of Monstro.
Word of God: According to an interview with Nomura, the encounter with the Bonus Boss called Unknown is canon for all of the characters. It's supposed to happen just before each character heads to the Keyblade Graveyard for the final time.