I rolled a 4 vs. a sanity score of 75
Absolutely awesome! You have captured his sanity shatering persona well. Now you will be the first on his list of souls he must devour for the sake of the end of all mankind.
Overall I really like the background and the feel of it but the foreground could use more work. Remember Cthulhu is under the ocean. So the water is a bit more murky. Maybe adding more of a blue to the foreground so it all looks submerged.