Check out this Adventure Time: The Enchiridion Limited Signed Edition. It is two books in one. The Enchiridion ancient hero tome on one side and Marceline’s childhood diary and scrapbook on the other. Mathematical!
It also includes a signed bookplate. It is written and signed by the real-life father-and-daughter team that voices Marceline the Vampire Queen and her father Hunson Abadeer, Lord of Evil.