He is not as omnipotent as a lot of people believe and there have been characters that have successfully been able to hold him back, not only that but he was also beaten by a mortal (Stanford Pines). All of his feats and accomplishments in the show only involve manipulating things on a planetary level, such as the town of Gravity Falls, and he was ultimately defeated by humans and an advanced machine made by them. I guess it would be accurate to place him at planetary level.