Katy Perry's lawyers sent a cease-and-desist to Shapeways for selling 3D models of shark costumes similar to the ones used in Katy Perry's 2015 Superbowl halftime performance. In this Make essay, Michael Weinberg of Public Knowledge argues that the cease-and-desist probably wouldn't stand up in court (even though Shapeways complied with the demand).
The problem with this is that courts have generally found that copyright does not protect costumes (even fairly creative ones). Essentially, courts have lumped costumes in with other kinds of clothing and considered them all the kind of "useful article" that is beyond the scope of copyright protection. If you are curious, that use in this articles is things like "preventing you from being naked" and "keeping you warm."
There are some legal theories that could be put forward to try and get copyright protection for a specific costume, but they mostly come into play when there are elements of a costume that could exist independently of the costume or when the costume is tied to a character developed in a book, movie, or play. It would probably be a stretch to put Left Shark into either of these categories.
An additional note is that even if the Left Shark costume is protected by copyright, that doesn't automatically make Katy Perry the owner of that copyright. But let's set that aside for now.
