Gravity Falls and TAWOG Movie

Gravity Falls and The Amazing World of Gumball Movie (known as Gravity Falls: The Movie) is a 2018 crossover movie idea. Like Batman vs Superman and Arrow and Flash, the movie has several appearances of characters of another universes. Actually, is a in-progress fan feature film. Probably will be a fantasy-adventure-drama-comedy film, starring as principal characters Dipper and Mabel Pines and Gumball and Darwin Watterson.
Sinopsis:
It all starts with the oldest of all legends knewn. 
Forever in existence, there was two kingdowns. Darkness and Light. Both balanced the pure and impure of Universe. But, after centuries, creatures of shadows rose in the worlds and only light could defeat so much power. The leader of these creatures was Harpaxolix, the giant wolf-dog. He was defeated by some fellas named Henry and Iris Pines and their good partner Lord Daniel Watterson with a magic crystal weapon. Harpaxolix vowed to return after centuries and have revenge destroying their descendents. Unfortunately, the crystal weapon was destroyed, and his last fragments were saved in powerfull lockets. Only the Pines and Watterson's descendents would find the lockets, finally saving the worlds of eternall darkness.