Wouldn't a prominent "I don't have anything to do with Disney" do it?

Steamboat willing entering the public ___domain would not allow you to create the movie "Mickey Mouse joins the Pirate Party"

But I believe you could make "Mouseman Joins The Pirate Party" and use drawings based on (or directly lifted from) Steamboat Willy itself, no?

If you lift the images of the strange mouse/person hybrid directly from Steamboat Willy, I would expect that to be legal. But I'm not sure if you could draw your own or not, could Disney have a trademark on the general likeness of the mouse man? I couldn't say. That said, parody/fair use would probably cover your ass for that in practice.

See https://fairuse.stanford.edu/case/klinger-v-conan-doyle-esta...

I would expect drawings based solely on thr Steamboat Willy work to be okay. The sequels start new timers on new characters or qualities, they don't extend the copyright on the original work. of course, IANAL.

Maybe explicit branding differentiation, in the style of "Disney's ____" already used to make for distinct branding from other public ___domain retelling. "Marvel's Superman", that kind of thing.