You can write a novel about a fear-based evil clown monster named "Centsmarty" that pulls kids into the sewers and does horrible things to them, and sell it all

You can write a novel about a fear-based evil clown monster named "Centsmarty" that pulls kids into the sewers and does horrible things to them, and sell it all you want. Plot is not copyrightable. It just can't contain any uniquely identifiable sentence fragments from any other novel. And you know people will be checking it particularly closely against the sentences in "It". And you'd better be sure not to say "Pennywise" anywhere, as that would be a trademark character. The bridge of the Enterprise-D is a trademark set design.