Every time you enter a new floor, the previous floors rooms are reset. As Sora and the gang advance through Castle Oblivion, they begin forgetting important things. Meaning, they forgot how they set up the rooms and need to set them up again.
Once you know the basics of the plot, if you start Sora's storyline over, it becomes hard not to notice that pretty much every world's modified subplot deals with the manipulation and falsification of memories. Considering the circumstances, it is entirely possible that Namine is trying to send coded warnings to Sora that he's being brainwashed.
It isn't until after you play through the game that you realize Aerith's speech to you at the beginning of the game may be Naminé sending a direct message to Sora, warning him of what lies ahead. Naminé is shown to be able to directly influence characters she creates, and Donald and Goofy tell Sora that they only saw him standing there by himself.
The Riku Replica's bizarre Jerkass behavior and desire to fight Sora for what appears to be no good reason should send up red flags that he's a fake, but doesn't because this is exactly how Riku acts throughout the entire first game. The subject of his anger at Sora has simply been changed from Kairi to Naminé.
However, it does seem to be a case of Flanderization...which, of course, also makes total sense given that Naminé was made to re-arrange his memories so that this would be the case. It's the same with Sora...Kairi is deemed the most important person to him, but Naminé starts to exceed that as the only important person to him the more fake memories based on his feelings for Kairi that are planted in his head. Both Sora and the Riku Replica are flanderized so that they are total puppets to Naminé...and thus, to the Organization.
Marluxia's Viewer Gender Confusion makes a whole lot of sense when you consider that Marluxia was originally conceived as female.
It's been noted that Larxene seems more like just an Alpha Bitch to the point of being Laughably Evil when around her fellow Organization members, but suddenly becomes extra-evil up against Sora, Donald and Goofy. Then you realize that Larxene is a sadist who gets off on inflicting pain on others' feelings...and the rest of the Organization don't have true feelings, just like her, so she has no reason to go as far in being cruel toward them. Even in RE:CoM, a moment is added when after taunting Vexen and causing him to shout at her, Larxene looks disappointed and says "Predictable response. Forget it. Men without hearts are so boring".
For the I.5 HD ReMIX, the fandom rejoiced when Kingdom Hearts I received re-recorded tracks - and raged upon learning that Re:Chain of Memories not only didn't receive re-recorded tracks, but it didn't use the already re-recorded tracks for I - instead, the HD version of Re:Chain uses the PS2-generated songs from the original release. Then you remember: this is not actually one of Sora's adventures, it's an imitation of his previous adventure. Castle Oblivion just couldn't get the audio right. The exception is the battle with Marluxia: the... last? phase of the fight does receive a re-recording, signifying that he's breaking free of the imitation and finishing his adventure properly.
Also note that "Lord of the Castle" (the re-recorded song) is the only one that wasn't in the GBA version of the game.
In Kingdom Hearts I, the Powerwild and Bouncywild Heartless were found in the Deep Jungle world. Because the rights to Tarzan were lost before Chain of Memories, those Heartless are now found in Olympus Coliseum; the only world not to have any world-exclusive Heartless in KHI.
In Reverse/Rebirth, Riku gets pre-arranged decks for each world (and each boss fight outside of the worlds). In Wonderland, Riku gets an extraordinarily sucky deck with less cards than normal and no cards above 5, whereas in Halloween Town for example, Riku gets an awesome deck with plenty of 9's, 7's and 0's. The fridge brilliance here is that Riku gets his power from Darkness. In a saccharine world like Wonderland, Riku is significantly weakened, while in dark and spooky Halloween Town he is significantly stronger. It goes even deeper, too: The mechanics directly support this, and so in Halloween town it is a piece of cake to break enemy cards and activate Dark Mode, whereas in Wonderland it becomes nigh impossible unless you carefully manage your deck.
In the Re:chain remake, several of Sora's Sleights were changed, giving him attacks like Magnet Spiral, Firaga Burst, and Freeze. Not to mention his numerous "Raid" variants, Holy, and Tornado. Now go play Birth By Sleep. Those are Ven's attacks — Sora's heart is reacting to Ven's sleeping body inside Castle Oblivion, and the deeper he goes, the more of Ven's abilities he gains access to. This is also why Sora loses those attacks come Kingdom Hearts II.
There are a lot of subtleties to the way cards are used by the various characters in this game.
Notice how only humanoid bosses use red and blue cards instead of the black cards used by the Heartless and (most) Disney bosses.
In addition, the only characters who use cards that don't just represent themselves is Sora (and Riku, but only with enemy cards). What's Sora's special power, again? Linking his heart with others.
In Reverse/Rebirth when Riku was being Mind Raped by Zexion and was thrown into an illusion that made him think he drowning in light, which is implied to have the ability to actually kill him off if Riku gave into it. Now Riku's in a position that if no one snaps him out of it, he will die. Of course Namine saves him and all, but where was the one who told him "You're not alone" in Riku's hour of greatest need? It might not be horrific to some, but the idea that everybody's childhood companion Mickey Mouse left someone to die is rather unnerving.
Add to that the fact Mickey later said that he originally believed that all darkness was bad no matter what, that includes those who wield darkness. Though the asshole other king (banished or not) in the room was kinda distracting.
But since it was only an illusion, it might not have physically harmed him, or perhaps Mickey couldn't tell he was in true danger.
Additionally, Mickey is a wielder of light. Illusion or no, he may well believe that there is nothing he can do against light except pray Riku has enough darkness to fight it.
These are all great theories, except there's one problem here. Mickey is unavailable during this time due to having to use up a good amount of his power to save Riku from Ansem; which left him cut off from Riku for awhile since Mickey was still in the Realm of Darkness at the time and not physically there to begin with. He couldn't have helped Riku out during this time even if he wanted to.
Do you remember that part in Agrabah where Aladdin tricks Jafar into using his second wish? Yeah, no. Jafar never actually said "I wish..." so if anything, HE tricked Genie into doing crap for him for free.
However, Genie considered saving Aladdin's life in the movie as using up a wish, so maybe those rules also hold in this game.