Not sure, also at the end of stakes and marceline is singing everything stays, there's a vision of a vampire visiting, I think, her mum, is it marceline? If it is, I have to say that she looks weird

It is either the vampire king or her mom. Because at the end of stakes she sings a song and shows her when she was a little girl on her moms lap.

The Vampire King, probably some kind of psychokinesis since he wasn't too far away, and we know he can read and enter people's thoughts, and even sign a book for Peppermint Butler with his mind