Background: Bill cipher was relatively normal for a pandimensional being. He was a madman, demented, and evil. What he wasn't, was all knowing. In the future, however, Dipper destroys him by opening him to all dimensions at once, driving him into eternal madness.
It only goes downhill from there. His already enigmatic mind is thrust into ever-constant chaos. years later, the chaos, running out of options, becomes what resembles normal. Do not be deceived by the shell of sanity. Beneath lies a true storm.
Personality: On the outside, relatively normal. On the inside, you'll go mad
Apearance: He resembles bill cipher being summoned. He has swirling galaxies throughout his being, and his eye is blue, as if he were making a deal. Surrounding him is a blue glow.