What happens when Cthulhu is released? A DM’s Guide
|http://goblinpunch.blogspot.com/2015/07/what-happens-when-cthulhu-is-released.html
Step one: “Every sentient creature on the planet must save or go permanently insane as the Cthulhu’s supersentience rips through their own, like a cruise ship powering through a narrow canal. ” Sounds like a good start.