This is my thought. Arcane and Mystic are synonyms. Whilst some of the subclasses were clearly needed, such as the specialist wizards missing from the PHB, some of the others were probably just a case of throwing stuff at the wall and seeing what sticks. So Mystic Arts monk may well be a...
Beginning? It feels like 1979 all over again to me! I really missed that 1st edition wacky crossover spirit. After that D&D started taking itself far too seriously.
For 5.5 Cthulhu has to go in Ravenloft, because that is the brand for D&D horror. They are not going to release a book for non-Ravenloft horror. This book will work just fine for that, no one is required to use the Ravenloft setting. And they are not going to release another Deities & Demigods...
Got to consider the chronological order:
Cthulhu was added to the game.
Cthulhu was removed for copyright reasons.
Hickman writes a Dracula spoof called Ravenloft. He decides to change names.
TSR creates a World of Darkness competitor incorporating Hickman’s Dracula spoof. It adds in a lot of...
There was a court case with Chaoseum, who had rights to Call of Cthulhu RPG. They had to remove the Deities & Demigods mythos chapter. The Moorcock chapter was cut too for related reasons, so they are both only in the fist printing (which I used to own 😡).
There was a separate court case with...
The thing is, every time he wakes up he trashes the planet. So he must get through a lot of planets, and R’lyeh has been in a lot of places. Ravenloft is probably the first place he can’t completely trash.
It also has Cthulhu as a dark lord (visible in one of the images). I assume there will also be a R'lyeh domain for him to sleep in.
But Yithian do have a lot of story potential, both for body swapping story lines, and just being incomprehensibly alien, without actually being evil.