Alright my theory is the lich is an alternate dimension version of Finn. His direct opposite. Because you know finn is the reincarnation of all that is good. So his opposite is pure evil. So the lich or alternate finn came into after jake had a traumatic death that had that dimension finn snap. So he ventured to find a way to see if he could bring jake back to life. And in his search for a solution through magic he loss control and was driven insane by never finding a solution. went mad like simon did the crown and starting seeing no purpose or meaning to life. In his lost sanity He decided to find golb and make deal with Golb to go to different dimensions to find a new jake to live with . But was tricked and instead was turned into the lich bent on destruction as pure evil. Jake was finns anchor in being a hero. With out him and losing jake at a young age made finn go down a dark path
ADVENTURE TIME! ⚔️ w/ DEV THE LEGEND AND JAKE THE DOG! #adventuretime #finnandjake #artlife #procreate #legendaryart (at West Jax) https://www.instagram.com/p/CpnIEfzraPO/?igshid=NGJjMDIxMWI=