Kingdom Hearts 3: 13 Ways To Include Every Pixar Movie
4. Monsters, Inc.
How: A world and/or summon.
Disguised as monsters, Sora, Donald, and Goofy could find themselves in Monstropolis just in time to come across Mike and Sulley during their time with Boo in the original film. With a great setting, a simple premise, and clear villains in Randall and Waternoose - who could, perhaps, be attempting to harness Heartless in their quest to power the Scream Extractor - Monsters, Inc. has every opportunity to deliver an amazing world.
Beyond that, should the creative team want to bring characters introduced in 2013's Monsters University into the fold, like Art, Sora could leave Monstropolis with the power to conjure up and open a door in the middle of battle, allowing any number of popular minor characters from the franchise to show up for a surprise cameo to help take down Heartless.