-The Roxas fight in KH2FM was originally planned for the original KH2, but due to time constraints and all that jazz, it wasn't put in the original.
-The original 1,000 Heartless fight looked much harder, with a barrage of familiar Heartless from KH1, such as the Wyverns, Behemoths, and then all the other Heartless that were there as well.
-KH2 was most likely planned even before KH1 released, due to the Menu Trailer that plays in KH1.
-Deep Jungle has never made a appearance outside of the first KH because the rights were taken away or something.
-Sora may have never existed because of how Mickey was the original planned protagonist.
-Cloud in KH1 was also meant to represent Vincent.
-Kairi cannot wield a Keyblade, for she only borrowed the gayblade from Riku.
-Apparently the Dark Side boss fight at Destiny Islands after the world is beginning to get swallowed up was supposed to have you use the Wooden Sword and not the Keyblade.
-ENDLESS, a word that popped up with NOBODY and HEARTLESS in the KH1 secret ending may have been a type of enemy, or not. But it hasn't been mentioned in the series since.
-Bahamut was a planned summon in KH1, but since he would be to big for the screen or whatever, he was scraped.
-Supposedly, Oathkeeper represents Kairi, and Oblivion represents Riku.
-When KH2 was being translated into English, some things in the game were changed. i.e. Xigbar's sniper ness ness, the Hydra's blood or something was changed to smoke, and Axel's death was made "more suitable for a younger audience"
-Atlantica in KH2 was a major fail
-Kairi in the BETA trailer for KH1 looked like a cross between a Gorilla and a man, at least, in the face area.
-Disney owns every single bit of KH except the FF Characters. Those belong to SQUARE.
-Namine aged from CoM to KH2.
-Many people in the KH Community hate Kairi
-Water was originally a spell for KH1, but was scrapped.
-Final Mixes will never be released in America because the Japanese are douches.
I'll probably think of more later