The Lich's History
The Lich is the main antagonist in Adventure Time, he is an ancient cosmic being who is the manifestation of the inevitable death of all things.
His essence was deposited on Earth millions of years before the start of the show via a catalyst comet, but came into physical being near the end of the Mushroom War from a "mutagenic bomb" after he possessed a person who had been submerged in mutagenic waste.
In the episode "Gold Stars," the Lich implies he is older than existence itself, a survivor of a time "before there was nothing." After that, in some way, his essence was transferred to a catalyst comet, whose task was to kill all living beings on Earth. The comet seen in "Evergreen" is bared a resemblance to the Lich, as evidenced by its green coloration and horn-like flames, and was implied to have caused the K–T extinction event that killed the dinosaurs. The Lich was later unleashed onto the world from the Mushroom Bomb during the Great Mushroom War.
At some point, he attempted to destroy all life but was defeated and imprisoned within amber in the Candy Kingdom's tree by the hero Billy many years ago.
In "Mortal Folly," after being freed from his prison by using a spell to take control of a snail, the Lich sets out to regain his power and destroy Ooo, but his body is destroyed by Finn, who uses the sweater Princess Bubblegum gave him to rip off the top of his skull—collapsing his entire body.
It is then revealed in "Mortal Recoil," however, that the Lich's disembodied spirit survived and took possession of Princess Bubblegum's body. The Lich was inevitably defeated by an unnatural team-up of Finn and the Ice King, causing him to end up possessing the snail that initially released him from the amber.
In "In Your Footsteps," after going into hiding in his snail vessel, the Lich arranged for a bear to trick Finn into giving him the Enchiridion for his master plan: to attach the jewels from the various crowns of power, most of which are worn by the princesses, to the book's cover and create a portal to the Multiverse, and ultimately the Time Room, the domain of the omnipotent and wish-giving entity Prismo.[5]
In "The Lich (episode)," having taken Billy's body as his own, the Lich attempted to achieve his plan of wishing that all life was eliminated. The Lich's scheme ultimately failed, however, when Jake used his own wish to alter the Lich's original request; Jake wished for the Lich's original wish to be retroactively changed so that Finn and Jake would return home safely. Originally, Finn had wished that the Lich had never existed, creating the Farmworld timeline, a timeline where the Mushroom Bomb during the Mushroom War was never set off, thus the Lich never came to be. However, Farmworld Finn wore the Ice King's crown and crushed the bomb that released the spirit of the Lich which went on to possess the body of Farmworld Jake.
Before the events of "Wake Up" and "Escape from the Citadel," his purpose null and void, the Lich remained trapped in a catatonic state within Prismo's chamber. But when Finn and Jake attempted to commit a cosmic crime in order to gain access to a multiverse prison called the Citadel, the Lich kills Prismo's physical body to reach the structure with the intent to corrupt it and its prisoners. However, having completely rotted Billy's remains off, the Lich is subjected to the regenerative properties of the Citadel's Guardian and is turned into a harmless giant baby. The giant baby is then entrusted to Tree Trunks and Mr. Pig who named him Sweet Pig-Trunks, or Sweet P for short.[6]
In "Gold Stars," though haunted by fleeting recollections of being the Lich, Sweet P has no memory of his former identity. However, it seems that the Lich can briefly reemerge whenever the child is threatened and under severe emotional stress, as shown when Sweet P is threatened and mocked by the King of Ooo and Toronto, during which the Lich implies he is older than existence itself, a survivor of a time "before there was nothing."
In "Crossover", Farmworld Finn (under the influence of the Ice Crown) and the Lich-possessed Farmworld Jake were using their world's Enchiridion to create a portal to the Multiverse. Prismo, concerned on the matter sent Finn and Jake to the Farmworld to stop/cure them. Farmworld Finn and the Jake-Lich went on to successfully open the portal. Finn's grass arm then attacked the Lich and chopped off his hand. Jake pushed the hand right next to the portal, where it duplicated and disappeared into every dimension, including the timeline of Finn and Jake.
In "Whispers", Sweet P ran away from home because of his nightmares and found Finn and Fern. The group could not leave the area that night and slept there. Finn woke up only to the Lich-possessed hand of Farmworld Jake. It is revealed the Lich of the Farmworld timeline has the same consciousness of the Lich of the standard timeline, having memories of the times he faced Finn and being aware of Sweet P's origins. The Lich hand referred to Sweet P as his son then left to go to his well of power. At the same time Sweet P said the same words, Finn followed the Lich to the well, only to fall into the pit hanging by one hand. The Lich then said that Sweet P is part of him and will eventually be swayed to come to his side. Sweet P then arrived, excited by the Lich, declaring them "twin kings of ruin." Sweet P, however, declared he is no king of ruin and slayed the Lich hand with a sword.
In "Come Along With Me", 1000 years in the future, an older, massive Sweet P is seen roaming Ooo around Mount Cragdor.
In "Together Again", it is revealed that the one who was truly in control of the Dead Worlds was not New Death, but the Lich, who manipulated him and then possessed him. Being in the form of the hand that appears in "Whispers", it is unknown if that was the same hand or a new one that could appear in the Land of the Dead because of the events in Farmworld. By the influence of the Lich, New Death starts destroying dead worlds, which means that souls couldn't reincarnate into new beings, so new life would stop to exist. Thanks to the item called the Kiss of Life, given by Life herself, Mr. Fox managed to kill New Death and once more stop the Lich. After that, he tries to manipulate Mr. Fox who became Mr. Death to place himself as his right hand, but he is quickly crushed by Jake and thrown away into the darkness. The Lich was the last opponent of Finn and Jake, before they reincarnated into new beings.
