You were Gideon Glyfool's older brother/sister.

Gideon called and made a deal with the demon of dreams and the god of chaos, Bill Cypher, but you didn't know about it.

One day you entered the room of your younger brother, who was 13, to invite him to dinner, but found him in a very shocking situation. Gideon was standing next to some kind of flying yellow triangle with one eye, which, after some exchange of remarks, turned into a human version of himself. This was Bill Cypher. Bill was now a tall guy with yellow hair and golden eyes. Neither Gideon nor Bill have noticed you yet.