In [Call of Cthulhu], what's your favorite mythos monster to play as a Keeper

… and why is it the color out of space?

Can be extended mythos and other rpg systems. Not counting mythos deities. Bonus points if you include scenarios (please hide in spoilers).

Should be pretty clear what’s my favorite. It just lends itself to pure cosmic horror in which the investigators can’t really win and can’t really understand the entity.

Examples

- Dying of St. Margaret - Dead Light - Machine Tractor Station Kharkov-37 - (a hack of the Corbitt house I wrote)