This is confusing to me. If copyright is up on Steamboat Willie, producing derivative works based on Steamboat Willie has to be allowed, so original content that remixes and adds to Steamboat Willie to make a new cartoon must be OK.
And there is such a thing as fair use in a trademark. Being descriptive is fair use of a trademark. You can market your breadbox as being compatible with Acme Bread. And you can describe your Sherlock Holmes book as containing Sherlock Holmes and as an extension to the public domain canon.
I don't see why Mickey Mouse gets special treatment just because he's also on logos and such. Disney, at the least, is forcing a conflict between trademark law and public domain law to see what it can get away with.
https://upload.wikimedia.org/wikipedia/en/d/d4/Mickey_Mouse....
https://images-na.ssl-images-amazon.com/images/M/MV5BODZhY2E...