Gravity Falls - One Year Later
"Dipper!"
He ran on ahead, exploring the area to see if anything had changed in the woods he had become so intimate with. He stopped at a familiar sight. Mabel catches up to him and to see what he is looking at.
"Dipper-" Mabel began. Dipper put his arm in front of her to tell her to look.
She sees what is lying in front of them. The only physical remnants left of the triangular demon who haunted them just last year. They gaze at it for a few minutes before Dipper says "Come on, Mabel. Let's head back to the Shack."
He begins walking, but Mabel stays, looking back at the statue. She could almost hear the song that Bill sang, all those months ago.
"We'll meet again. Don't know where, don't know when! Oh, I know we'll meet again some sunny day!"
She approaches it, only to see its hand held out, as if to suggest a deal. She looks down at her hand and slowly puts it onto the statue's.
The air is filled with the sound of a very familiar cackle. Bill had returned.

Sorry, it's so short. If you couldn't tell, this was based on the fan animation of the same name on YouTube. If anyone wants me to continue this, I will.