The Great Old Ones are a group of unique, malignant beings of immense power. They reside in various locations (buried beneath mountains, sleeping under the sea, etc.), and once presided over the planet as gods and rulers. Looking upon such a being can twist and distort the fragile minds of the mortals. Use this table to generate what exactly happens when you look upon a Great Old One.
https://www.dndspeak.com/2022/02/100-effects-from-looking-upon-a-great-old-one/