This is going to get me put on a watchlist...

• Six String Samurai: The boy
• A Boy and His Dog: The boy
• Time Bandits: The boy
• Brazil: Robert De Niro
• The World of Kanako: This would be an unhinged fever dream no matter who is picked. I'd like to propose Ogata for shock value in a particular scene, but I think either Kanako or the main character detective overall work better
• The entire Saw franchise: Jigsaw
• SLC Punk: Heroin Bob
• Tokyo Gore Police: Key Man
• Hook: Everyone in the real world is human, everyone but hook in Neverland is a muppet, and Robin Williams starts human but by the end is a muppet
• Les Mis: Javert
• X: The old woman
• Swiss Army Man: Daniel Radcliffe or Paul Dani could work here but I prefer the dead body
• Any zombie movie but people start human and turn to muppets when bit. I nominate - - - Train to Busan
• Audition (1999): The main character