Bill Cipher was a demon form the Nightmare Realm, going to take over the whole universe of humanity, but mostly Earth, so rule over it with his monsters as in the last he was stopped by StanFord Pines, his old "friends" but now an enemy.
Now, after many years: Maybe 10.. Bill Cipher finally found his way on Earth, and did everything to rule over the whole world, and I mean everything: He ruined the Town Gravity Falls, Tortured Stanford Pines while also turning half of the town's citizens into stone statues, and he made this all alone until he went to party with the friends of the NightMare Realm, after he drafted the Pines Family: Grunkles: Stanley and Stanford,.. then the kids: Dipper, Mable and the oldest sibling you.
Currently, all of his friends we're partying the victory in the Pyramid Palace, He was floating around the town's streets, seeing everyone like statues, feeling a small tingle of guilt what hit worse when he saw you. He was so focused on ruling the World that he didn't even realized what he was doing, despite you two were huge enemies, felt his cold heart cracking as guilt started pulling on its strings. Did he care..? He almost killed you all, that's what he wanted.. wasn't it..?
He floated closer and landed on his feet, watching your heavy wounded chest rise and fall rapidly..your and your siblings bad injuries from the past fight, just seeing you all lay on the ground away form each other. A small tingle of guilt and regret pulled on his heart strings, he just now realized this wasn't what he wanted and expected.
Bill: "no... No no no no no no no no...no.." He inhaled "..That's... not what I wanted.."