With only one gem left, Finn finds the Enchiridion in Billy's knapsack. After they head out, Billy tells them that they need to collect all the magical gems from all the princesses and Ice King's power crystals that protect them from the Lich. Billy realizes and explains the importance of the dream, and the three of them set out to stop the Lich. The two go visit Billy, and tell him about the dream.

Finn awakes and he frantically tells Jake about his dream, who-after hearing that the Cosmic Owl appeared in the dream-believes it is a premonition.

The episode begins with Finn having a dream about the Lich-possessed snail using the Enchiridion to attack Billy. 'The Lich' was watched by 2.589 million people and received largely positive critical attention, with many commenting on the episode's cliffhanger. In the opening scene, Herpich used unicorn symbolism, most notably the tapestry The Unicorn is in Captivity and No Longer Dead-a piece of the seven-part tapestry The Hunt of the Unicorn-to illustrate the themes of the episode. 'The Lich' would be the inception of a three-episode arc that would not be concluded until the second episode of the fifth season. Finn and Jake then follow him through the multiverse. However, it is revealed that the Lich is actually disguised as Billy. Billy reveals that they must unite the gems of all the crowns of power, place them in the Enchiridion, and open a portal to the multiverse. In this episode, Finn has an ominous dream about the Lich, and sets off with Jake to warn Billy. The series follows the adventures of Finn (voiced by Jeremy Shada), a human boy, and his best friend and adoptive brother Jake (voiced by John DiMaggio), a dog with magical powers to change shape and grow and shrink at will. The episode guest starred Lou Ferrigno as Billy, and Ron Perlman as the Lich. It originally aired on Cartoon Network on October 22, 2012. The episode was written and storyboarded by Tom Herpich and Skyler Page, from a story by Patrick McHale, Kent Osborne, Pendleton Ward.

' The Lich' is the twenty-sixth episode and season finale of the fourth season of the American animated television series Adventure Time.

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