Steamboat Willie Enters Public Domain - "the undying love of mickey mouse"

For that we can take from Disney themselves ironically, all their adaptations have a "Disney's" (or "Walt Disney's" when he was still alive) in front of them for this reason, you're telling everyone "this is my own original version".
Also some people DO believe Mickey's name in that short is "Steamboat Willie" for some reason, i've seen a fair share of "no you can't use the Mickey Mouse name cause he's called Steamboat Willie in that short!!", ignoring of course Mickey's full name being in the movie title card and the other two now public domain movies also calling him Mickey Mouse.
So yeah TL;DR is just add a "[Your Name]'s" in front of whatever you do with Mickey and you're golden, again provided Disney doesn't get uppity about it in a "screw the rules i have money" fit.

The biggest thing from what I can tell is you have to be super careful to make sure you're not trying to make it seem like you're affiliating with Disney in any shape or form. One thing I am seeing some people do with their own takes on Mickey is they either avoid using "Mickey" entirely or they call him "Steamboat Willie" as if the name of the animation is his actual name.