Hex 2412 of Isle of the Unknown, Geoffrey Mckinney's crazy-as-hell new hexcrawl sandbox, contains a 6' tall duck-man (with, if the illustration is to be trusted, very nice abs). Killing the duck-man opens a gate to the Demiplane of Ducks, thus finally providing an in-game rationale for torturing my players with Howard the Duck bits. I bet the Demiplane of Ducks even has its own Demiplane of Dread, where Count Strahd of Ravenloft becomes Count Duckula of Duckuloft.
Now, you probably wouldn't do that. But you could do that. And that is awesome.
Thank you, Geoffrey.