Marshall Lee has pale skin and two bite marks on his neck and carries a base guitar like Marceline, but however, he has short black hair, a red plaid shirt and blue jeans with blue/white sneakers.
Marshall Lee only made an silent first appearence in "Fionna and Cake" at Prince Gumball(Fionna's love interest)'s party. He just does a sign of horns sign.
He returns in "Bad Little Boy" where he manages to chase Gumball away from Fionna and take her to Lumpy Space Prince's party where he tries to make Fionna admit she like-like him. He goes too far as stealing Cake and almost dies in sunlight, but when Fionna does, he reveals he was joking and faking. Fionna in anger and emotion, beats the snot out of him.
In "MCF: A Musical Nightmare", he teams up with Wormy(Jessy and Aaron's sandworm 'son'), Holt Hyde(Jackson's Hyde form), Eden, Jessy, Emmy and the Predators of Predator Island to stop Mafiafas and Damien from taking over the world and get Jessy's memories back.
- Marshall Lee's voice in MCF: A Musical Nightmare is simular to Jake Long's which the authoress thought he'd sound like before "Bad Little Boy."
- Marshall Lee can be flirtatious towards girls.
- At night time, Marshall's skin turns a pale green.
- In most stories, Marshall Lee has been paired up to be best friends with Holt Hyde/Jackson Jekyll from "Monster High". This was before "Hotel Transylvania" came out and Jonathan seemed to replace Marshall.
- Marshall Lee, Holt Hyde, and Wormy are in a band called 'The Dukes of Royale'. It is not clear whether he or Holt is the leader.
- It is unknown whether Marshall Lee would be in other MCF cases.
- MCF: A Musical Nightmare