Ursula doesn't remember Sora, Donald and Goofy, although other resurrected characters (Jafar, Oogie Boogie, Maleficent) do. Maleficent, who returned in the exact same manner as Ursula (using the powers of darkness), does remember them, so there is no reason Ursula shouldn't.
When you go and talk to Sephiroth for the optional fight, Donald and Goofy are there in the cut-scene, however, when the fight starts, the two of them are now absent without any explanation at all.
In the trophy room at Olympus Coliseum, upon examining the Phil Cup Trophy and Pegasus Cup Plaque, it reads "Phil Cup Plaque" and "Pegasus Cup Trophy", which should be reversed.
Pete's journal entry in Pride Land claims he is 'aiding Scar's phantom'. However, Pete only appears during the first visit to Pride Land, whereas Scar's ghost doesn't appear until the second visit. Also, Scar's ghost is already mentioned before it appears (and before Scar is even defeated).
Organization members Xigbar, Xaldin, and Lexaeus' real names
are misprinted in the English version of the game as Bleig (Braig, Xigbar), Dilin (Dilan, Xaldin), and Eleus (Eleaus, Lexaeus).
In the Journal, it is said that Goofy made his first appearance in Two Weeks Vacation (1952). That first appearance was actually twenty years earlier in Mickey's Revue (1932).
When you investigate the seven rumors in twilight town, the word "bag" is spelled wrong after you let the dog out of the bag.
When Roxas sees Sora's memories in his dreams, he also sees scenes that Sora never witnessed, such as Jafar's line "The boy is a problem; he found one of the Keyholes" which was at Maleficent's council in Hollow Bastion. Sora was never present to hear Jafar say this line.
Scrooge McDuck's journal entry states that, 'Before the Heartless appeared, he was using the Gummi Ship to travel across worlds'. However, in the first Kingdom Hearts (2002) it is stated that, before the Heartless came, 'impassable walls' divided the worlds, making inter-world travel impossible. It only became possible after the emergence of the Heartless, who destroyed the walls.
In Port Royal, to end the curse of the Aztec gold everyone who has touched the golf must pay in blood. However, when Jack Sparrow tosses the coin to Will he doesn't cut himself to pay in blood as he does in _Pirates of the Caribbean: The Curse of the Black Pearl (2003)_.
It is clearly stated in the first game that Sora, Donald and Goofy must not meddle in the affairs of other worlds. All their actions in the various worlds they visit are to stop the Heartless and other foreign villains from meddling. However, in Atlantica, which is free from Heartless and also not visited by Pete or Maleficent, they have no problems interfering to help Ariel against Ursula.
Christmas Town is considered part of Halloween Town by the game's mechanics, even though it is clearly a separate world story-wise.
In Land of Dragons, after the Captain finds out Ping is really Mulan, he tells the rest of his troops "Move out!" He then leads the group away. However, after all the troops have passed by, you see the Captain following behind them at the back of the group.
Right before you play the "1,000 Heartless Challenge", there is a cut scene in which Mickey runs after Xemnas, leaving Sora, Goofy, and Donald behind. The trio is then surrounded by Heartless. There is a shot of Sora, who looks over his shoulder at Donald and Goofy. The shot then changes to Sora again, who runs to attack the Heartless. In these scenes, each character has their most basic weapons they start with in the beginning of the game.
In the ending when Sora is reading the letter from Kairi, they spell the word "starting" wrong. It is written "Now I will step forward to realize this wish. And who knows. stating a new journey may not be so hard."
After the Heartless damage the Winnie the Pooh book, Sora enters the book again. Pooh starts his "stoutness exercises". He first touches his toes, then lifts his right foot. The angle changes, and you see him from the back. Pooh touches his toes, and lifts his right foot again. It is obvious from the next few exercises he does that he should be switching feet.
When Luxord invokes the Pirate Code (the right of parlay) in Port Royal, Jack Sparrow accepts this. However, as stated in Pirates of the Caribbean: The Curse of the Black Pearl (2003), one must be a pirate for the Code to apply. Sparrow should have known this of course, and ignored Luxord's request.