Alien forms of gameplay/game design you've encountered?

[Brendan Byrd]

I can see a case where a DM has requirements about IP rights. If they do social media content based on DMing, write books based on the campaigns they run, or just publish gaming content, it would be reasonable for a rando DM that you meet at a game store or convention to get in writing that they're allowed to use your character and ideas from a game they run. Sadly, I can totally imagine someone playing a convention game with someone from Critical Role, and later suing them claiming ownership of something that made it on the show.

But even that extreme case wouldn't justify a "non transferrable to other tables" clause.

In those contexts it is understandable, and involves an agreement between the parties.

The instance that I encountered was 30+ years ago.
No informed consent copyright release form or NDA involved.