The enchirideon the hero book can be used to travail through time and space. The lich knowing he couldn't use any normal way to reach his goal he killed billy using his own skin as a costume to convince Finn and Jake to steel the gems that able the book to perform such a task. The gumball guardians detected evil within 'billy' destroying his face when it was completed. Yet since it was too late the lich open the portal to the wish maker. A god able to grant any form of wish. He was going to wish for the death of all life. Lich is deathless. Yet jake saved the day wishing for him to wish him and finn to return home.