clearstream
(He, Him)
If @teitan's point is that - restating slightly - copyright doesn't protect mechanics: then that is correct. On the other hand, copyrights are very much an example of IP. The exact wording of rules can be IP. The working of rules may - but is unlikely to be - a protected IP.I concur with your learned opinion, m'lud.
WoTC might someday claim that Umber Hulk is an unregistered trade mark, but it's never been used as a badge of origin by them so I think such a claim would be very weak.
It's quite possible that the Umber Hulk as a detailed concept (not the bare phrase) has copyright protection under US law. Certainly Umber Hulk artistic depiction will. But the idea of "a giant tunnelling insect-headed monster with hypnotic eyes" is not itself copyright protectable IMO.
(For anyone new: I teach IP law and contract in England)
"Umber Hulk", I don't really know about. They don't need to have registered it to be able to claim a trademark (although in some territories they would need to have claimed it as a trademark.)