Hard to say....
How i do the Kingdom Hearts Series (Hortonverse)
Changes in general
Don't make the stiff platforming.
Have the Game Collection have a Physical Release on Nintendo Switch instead of putting it on Cloud
Improve the animations and movement.
More clever and creative humor instead of vile gross out humor, toilet humor, crude, and bland for shock value.
Improve the Writing, Humor
KH1: Make Ariel a Princess of Heart instead of Alice Merge KH2's Atlantica with KH1's Atlantica only without Singing Minigames, Have the Disney Princes (Prince Florian to Aladdin), play a Role in rescuing the captured Princesses (Snow White, Cinderella, Aurora, Ariel, Belle and Jasmine) Either Fix Deep Jungle or replace it with another Jungle Themed World (Either The Jungle Book or The Lion King) have Chain of Memories be a DLC on Kingdom Hearts titled Castle Oblivion (Changes: Make it a normal KH1 Gameplay instead of a Card-Based Battle System, Have their be a Secret Boss fight since the Original Chain of Memories and Remake never had a Secret Boss, The Replica Program no longer took place. As such, the Riku Replica was never created, and Xion underwent backstory. Ansem actually fights rather than letting his Guardian do all the work, even if he just uses dark spells ITTL.
- Pull the camera back, similar to KH2.
- Add Quick Run in first game.
- Improve the Sora's clunky jump.
- Don't make stiff combat in KH1.
- Gummi Ship sections are fully unique and not generic.
- Make New Game+.
- Update the enemy HP bar.
KH2 Changes
Replace Atlantica with a Disney World that hasn't been in the Series (Either Atlantis the Lost Empire or The Emperor's New Groove)
Kairi gains her Keyblade at the beginning of
Kingdom Hearts II.
- Improve the dancer Nobodies of critical.
- Don't make the Dancer nobodies are cringe.
Give Sora the Synch Blade ability outside of Drive Forms.
Riku wouldn't be the only party member in the World That Never Was but Kairi also joins the Party making it for the First Time 5 Party Members but Donald and Goofy would still Switch out but before you reach to Xemnas Battle
KH2 make the worlds more interactable, creative, and open instead of just having linear hallways and uncreative.
Better story pacing (especially the Roxas segment) and better tutorials.
Tifa playing a role instead of being "just there" going on a Goose Chase.
The Anti Form mechanic. Allow it to be normally accessible, allow dark magic, use reaction commands, revert mid combat, use 4 drive gauges, not need party members, give it EXP points, and completely ditch the hidden anti points.
Improve the gameplay.
In this level battle system with canceling and reprisals.
Tech point system, to incentivize use of different mechanics.
Dodge roll at the beginning instead of getting quick run and dodge roll so late in this game.
Better explanation of game mechanics.
Turbo mode.
Improve the camera controls and combat interactions between party members.
Better tutorialization of mechanics like Drive and Summons and buff Dodge Slash.
Reaction Commands that require better timing.
Characters like Jack Sparrow's Crew (Joshamee Gibbs, Anamaria, Cotton and the Parrot, Marty), Governer Weatherby Swann, James Norrington, Murtog and Mullroy, Pintel and Ragetti would be added in Port Royal. Zazu would be added in the Pride Lands
Kingdom Hearts Days Between would be added as a DLC for Kingdom Hearts 2 (Which Includes the Pinocchio World that was scrapped from the DS version OTL)
Kingdom Hearts Birth By Sleep (Changes: Add in Both The Jungle Book and The Sword in the Stone (Which explores Merlin's Origins before he traveled to World to World and how he became a Recurring Character in the Series) (Added in the Capes for Terra, Aqua and Ventus's Armor, Laguna would be added in Mirage Arena as a Boss, Pleakey would've been a Character in Deep Space, Ventus would've acquired the Lightseeker Keyblade)
Kingdom Hearts Dream Drop Distance: Have the Game's Gameplay structure be Similar to Kingdom Hearts Birth By Sleep with Sora, Riku and Kairi having their Scenarios instead of just Two Playable Characters (I would've add in Treasure Planet as a Playable World not sure about the Rest of the Worlds maybe Save Tron Legacy's The Grid for KH3)
KH3 Changes
Have the Birth By Sleep 0.2 A Fragmentary Passage be a part of the Game and serve as a Tutorial
Use Music from Disney Movies Examples: I see the Light from Tangled and He's a Pirate for Pirates of the Caribbean
Have the game start development on Unreal Engine 4 from the Beginning
I would have at least Two or Three More Playable Worlds
Have Land of Departure appear on the World Map
Have the Anti-Aqua fight be Zodiac Aqua with less health and more moves and remove Demon Tower from Riku's section of the fight.
Don't kill off Kairi
Roxas, Terra and Xion have new Outifts
Make Mysterious Tower be a Playable Area in Twilight Town instead of a Cutscene World as was seen in the Jump Festa 2016 Trailer
Scala ad Caelum is the world that resides inside Kingdom Hearts.
Melody of Memory would be a DLC added in Kingdom Hearts 3
Sora and his party members walk in place when selecting the pause menu.
The Power of Waking is referred to as the Key to Return Hearts, a name it was called during conceptual phases of the canonical game, and is an actual Keyblade instead of an ability inside of Sora.
Have the Drive Forms and Reaction Commands instead of being replaced by Situation Commands
100 Acre Wood is expanded to be more of an explorable World with More Areas to explore and things to do
Improve the Graphics to a more True PS2 era Graphics like 2013 Trailer
Sora, Donald, and Goofy receive new winter-themed attires while in Arendelle.
Have Elsa and Anna as Party Members instead of Marshmallow.
Not sure what i would do with the DLC Remind either add it to the Base game or keep it like it is.
I would fix Arendelle so Sora Donald and Goofy would explore the Whole World and have them interact with the Cast and keep up with Anna, Kristoff, Sven and Olaf instead of getting separated