The rumor comes from Kinda Funny Games, which said Nintendo “approached Disney" about adding Sora from Kingdom Hearts to Super Smash Bros. Ultimate, but it was Disney Japan that “specifically” nixed the idea. Why Disney is loath to include the character wasn’t stated, but Sora has been requested by fans more than once (thanks, Nintendo Everything). The most recent character to be added to the game was Byleth from Fire Emblem: Three Houses in January. It’s been rumored more than once Crash Bandicoot will also be released as a fighter. Six more fighters are coming to the game with Fighters Pass Vol. 2, currently under development. It will run you $29.99 and each release contains one new fighter, one stage, and multiple music tracks. Those who purchase Fighters Pass Vol. 2 will also receive an exclusive costume for Mii Swordfighter, and the Ancient Soldier Gear from the Legend of Zelda: Breath of the Wild.
