ANOTHER FIRST AMENDMENT QUESTION THAT REALLY SHOULDN'T BE ALL THAT DIFFICULT

Some local government somewhere passed an ordinance outlawing clown costumes. There's a term in First Amendment law that I think inevitably means such a ban cannot stick. The term I am referring to is "content neutral." Here's my off-the-cuff, shorthand explanation of the concept: if you're going to ban a form of expression, the ban can't be based on the content of the expression. A ban of any form of expression must be content neutral to be consistent with the First Amendment.
So, as Professor Volokh points out, a ban of all masks can be enforceable. A ban of a particular kind of mask based on the content of the mask, however, is not content neutral and is therefore probably not enforceable consistent with the First Amendment.