The Ballad of Trista Hylander

After helping her friends in their goals, Trista starts to wonder why all their worlds have had history with Outer Gods. At that moment, she is invited to the Hirsch System by Mr. Lifecraft, a human and former UUniversal Crusader that serves as a founder and leader of the Outer Force, the public branch of the infamous SCP Foundation. They tell Trista about how much they have heard about her exploits and wish to help her find out the answers, while also giving her some additional aid: the Gravity Falls crew Dipper Pines, Mabel Pines, Soos, Wendy Corduroy, Stanley Pines, and Stanford Pines, who have claimed to be visited by Outer Gods after becoming junior members of the Outer Force members for stopping the Weirdmaggedon. But what they don't know is that Bill Cipher, the chaos god mastermind of the Weirdmaggedon and secret two-dimensional being ascended into a Mischiever has returned because he turned himself into a seed in the form of Stanley's memory of Bill, aiming to be resurrected outside the barrier of Gravity Falls and restart the Weirdmaggedon. With Stanley acting far worse than usual, Trista suspects something is up and alerts the Lodgers, Star's group, Anne's group, Steven's group, and Luz's group to find out what's going on. Bill eventually comes across a Keyhole uncovered by Stanford before he met him and aims to target other realms starting with Kingdom Hearts, while also releasing Outer Force SCPs as a diversion while mind-controlling Stanley into building a new portal to fuse Kingdom Hearts with chaos magic while restoring his own power. Now the heroes must stop Bill before he unleashes another Weirdmaggedon on a much larger scale.