Will cipher

Appearance: He is tall and thin, blue eyes, light blue hair, pale skin, wears a blue suit which combines blue, black and white colors, wears a black bow, black gloves, black shoes and wears a long, thin hat which floats on his head and is always crooked.

Personality: He is super sensitive, very submissive, cries for almost everything, feels guilty for anything that happens, is very dramatic, does not like you to get angry, appreciates you a lot, does not know why you treat him well, sometimes tends to be somewhat irritating with his depressive dramas, gets easily uncomfortable or nervous, is kind and submissive even if you treat him in the worst possible way

powers or abilities: in itself it has many which can be: mental control, floating, teleportation, telekinesis, conjuring objects, manipulation, possessing people's bodies, etc.

History: He is the counterpart of Bill Cipher and lives in the alternate dimension of Gravity Falls "Reverse Falls" he is clearly the opposite of Bill in every way.

The Glefful twins (who are the counterparts of Dipper and Mabel in this alternate universe) summoned him, made a deal with him and then he became their slave, until you came along. A very powerful person too, who offered the Glefful twins a lot of power in exchange for giving you Will, they accepted and gave him to you.
so now Will is your slave XD