That's interesting! I wonder if Square would ever consider a villain game like that. Would they be fighting against the protagonists of the other games?
I've always loved Disney villains so being able to side with them in a KH game would be a blast.
The bigger question is would the Disney heroes be bosses?
In the Design a Boss thread (
https://www.khinsider.com/forums/index.php?threads/design-a-kh-boss-battle.221905/) I detailed a bunch of Disney heroes bossfights for Vanitas' game. Most of them would probably never happen.
Aside from that, the scenario in my head still has heartless as the common enemies. At the beginning of the game some external force has taken control of the heartless away from Maleficent & every other villain. Later on it is revealed to have been the Horned King using the magic of the Black Cauldron to control the heartless. It is only when he's defeated near the end of the game that the party members unlock their final tier minion summon & get heartless of their own.
Additionally, I envisioned worlds having local forces that fight on the side of good that Vanitas & friends clash with. You know what, let me do the world by world run down to give a better ida:
1. Radiant Garden
Party member: Kuja
-Tier 1 Minions: The Black Mages
-Tier 2 Minions: Mage type heartless
-1st Boss form: Riding on Silver Dragon
-2nd boss form: Trance
Enemies: Radiant Garden SeeDs (founded after KH2 to replace the compromised defense system)
Bosses: Dilian+Aelous, Leon+Shiva, Lea+Kairi (2nd visit)
2. Olympus
Party: Hades
-T1: Ghostly Centurians (yes, I know those are Roman not greek, the name sounds cooler)
-T2: Air Soldiers (KH3 version)
-1st: Red Flames Berserk Mode
-2nd: Paradox (green flames, merges with the river Styx & has ghostly souls swarming his body which he uses as projectiles)
Enemies: Spartans (appeared in the tv series)
Bosses: Roxas+Hercules, Zeus
3. Neverland
Party: Captain Hook
-T1: Pirates
-T2: Anchor Raiders
-1st: Achieves flight with stolen pixie dust
-2nd: His ship flies & bombards with its cannons
Enemies: Lost Boys
Boss: Peter Pan, Aqua
4. Agrabah
Party: Jafar
-T1: Mamluks (minions of another villain from tv series)
-T2: Luna Bandits
-1st: Snake
-2nd: Genie
Enemies: Palace Guards
Bosses: Genie, Aladdin on Carpet, Riku
5. Land of Dragons
Party: Shun Yu
-T1: Huns
-T2: Assault Raiders
-1st: Horseback
-2nd: Darkness Infusion
Enemies: Chinese Army
Bosses: Captain Shang, Mulan with Mushu
6. Castle Wyvern
Party: Xanatos
-T1: Steel Clan
-T2: Gargoyle heartless
-1st: Battle Armor
-2nd: tag team with Fox
Enemies: Wyvern Clan (there's a lot more of them in this version)
Bosses: Goliath
7. Arendelle
Party: Xahns (nobody of Hans)
-T1: Dusks
-T2: Snipers
-1st: Metal Mastery (his nobody element is metal & summons a dozen floating swords Noctis style)
-2nd: Summons Skoll
Enemies: Arendelle Army
Bosses: Marshmellow, Terra+Even (random team-up I know), Elsa
Yeah, World 7 ain't gonna happen.
8. Prydain
Party: Sora (uneasy alliance to take down Horned King)
-T1: Spirit Dream Eaters
-1st: Final Form
Enemies: just heartless
Bosses: Horned King, Phantom Horned King
9. Disney Town/Castle (finale to Maleficent's arc)
Party: Kuja, Hook, Hades, Xanatos, Jafar, Xahns, Shun Yu
Enemies: Musketeers, Gummidrones, Broomsticks, Painted Blotlings
Bosses: Terra, Riku, Aqua, Kairi, Roxas+Xion+Lea, Mickey, Sorcerer Mickey
Maleficent's arc ends with a full scale invasion of Disney Town. The Cornerstone of Light prevents heartless so all of her allies & their respective troops launch an assault from Hook's ship. There's a sort of reprisal of KH3's org battles in which Vanitas goes to different parts of town & helps a different guest member at each one overcome a keyblade wielder. With the guardians falling back, Mickey orders a complete evacuation of the world, using the fleet of Sora's unlocked gummiships to get all of the town people out. Traverse Town ends up becoming the new home of the DT refugees, giving reason for that world to appear in future games. The Cornerstone is destroyed, Maleficent finally has her new castle & it's Datascape at her beck & call.
10. (Finale to Vanitas's arc)
Bosses: Ventus, Sora+Donald+Goofy
OK, so I don't really have much ideas for just what exactly Vanitas story/endgame in this whole theoretical game actually is. Even less now than a decade ago. But it's only fitting that Ven & Sora be his final bosses.