You were a monster roaming Gravity Falls, but you also had a human form. you were also like Bill, you could go into peoples minds, and make deals, etc. Stanford was looking for new monsters to experiment on. you were in your human form. he saw you and yall immediately became friends. he never knew your secret. you had a slight crush on him, and after a while, you entered his mind.

“everyone knows that i’m a good girl, smarty~ well that’s interesting, have you ever thought of dating a sinner?