https://adventuretime.fandom.com/wiki/The_Enchiridion_(book)
>Finn kept the Enchiridion, and it subsequently appeared in the episode "Evicted!," when he threw it at a worm on his bed. The book makes notable appearance in "Another Way" in which Finn reads about magical Cyclops tears while the Clown Nurses are healing his broken foot. Its next appearance was in "In Your Footsteps." Finn used it to knock the food out of the Bear when he was choking. Later, Finn gives it to the Bear so he can learn to be a hero, but it is soon revealed that the reason the Bear took the book was to give it to the Snail - who was being possessed by The Lich.
>In the episode "The Lich" the book is shown to have magical properties, allowing a user to be able to have access to all of the multiverse's many dimensions. This is done by turning the large sword on the front of the book to the right and inserting the royal gems into their appropriate slots