The Lich

The Lich (formerly known as The Lich King) is a necrotic villain in Adventure Time. His first appearance is in "His Hero" during a flashback about the adventures of the great hero Billy. He plays the main villain in "Mortal Folly" and "Mortal Recoil," where he nearly kills Princess Bubblegum. The episode "His Hero" showed that Billy cast him down, and "Mortal Folly" shows that he was ultimately imprisoned in a large glob of amber in the ancient tree that serves as the castle of the Candy Kingdom. After being defeated again in "Mortal Recoil," the Lich apparently continued to inhabit the body of the waving Snail, which appears in every episode.

Appearance
His first design had a more flattened, simplified look with larger eyes, downward-pointing horns and a different crown and robe. The design used in the series has a helm with curled horns, one of which has broken off, horrific green lights as pupils peering out of his empty eye sockets, and pale undead skin pulled tight against his noseless skull. His skin is frayed away from his lips revealing a wicked and perpetual grin. His arms are bare bones with various decayed tissues, and his skeletal hands burn with an eerie fire when he casts fire spells. The Lich is also remarkably large. In the flashback in "His Hero," the Lich was shown to be almost as large as Billy. Before the Lich was struck down by Billy, both of his horns are intact, so it is possible that it got broken off sometime during or after the fight. He also has intact horns in Princess Bubblegum's vision.

Abilities
Aside from his immortality, the Lich has a medley of unholy powers, most prominently the flames he generates around his hands that he fires at his opponents. Early on in "Mortal Folly," it was revealed that the Lich has the power to control people's minds, either through telepathy or spoken commands. Later in the episode as he makes his way into his lair he has the power to decay anything he walks on. Moreover, he has the ability to possess other people, as seen in "Mortal Recoil" when he survived by possessing Princess Bubblegum. He also has the ability to fly, and can kill or destroy virtually anything he comes into contact with. When he tried to cross Iceberg Lake, he inadvertently killed all the fish in the lake, and when he fought Finn, he caught Billy's gauntlet bare handed and turned it to dust. He is also able to implement necromancy, as seen when Finn and Jake entered his lair. While the Lich was possessing Princess Bubblegum, he shows powers of pyrokinesis, when he sets her room on fire with his mind.

The Lich sustains his massive strength by drinking from his Well of Power, a noxious, magic pool of glowing green liquid (which after possessing Princess Bubblegum, was substituted with a mixture of toxic chemicals such as gasoline, lighter fluid, bleach, and plutonium). While his power is truly a force to be reckoned with, the Lich has a few known vulnerabilities. His main weakness is the Gauntlet of the Hero Billy, a magical weapon that fires intense energy blasts. This weakness is now moot, as the Lich destroyed Billy's gauntlet with ease when Finn used it as stated above. Another item able to work against the Lich is the sweater Princess Bubblegum gave to Finn. Imbued with the power of "Liking someone a lot," the sweater protected Finn from the Lich's flames, and was later used as a weapon. With it, Finn was able to attack the Lich and reduce his body to dust. However, the sweater doesn't seem to affect the Lich when he's possessing the monster-formed Princess Bubblegum. The Lich is also unable to control a person's mind if they are wearing a certain type of magical jewelry. While generally impervious to physical attack, traditional methods may have some limited effect on the Lich, as seen in the flashback where Billy cast him down with a kick to the face.

Personality
The Lich is rather taciturn and speaks only in brief statements. Because he seldom speaks, his words carry great gravity. In spite of his intractability, he is visibly shocked when Finn survives his fire attack, and he laughs heartily when Finn attacks him with his sweater. He has only raised his voice once, when Finn asked the possessed Princess Bubblegum if everything was all right. He also has an apparent disdain for all living things, as Princess Bubblegum said that his only desire was to destroy life.

He is rather cunning, as he is cautious to protect himself from anything that has defeated him in the past, such as Billy's gauntlet and Finn's sweater.

Role in Ultima
In Ultima, the Lich King is an all powerful member of the Organization, and a recent member of the Inner Circle due to his immense power of darkness. Because he is Dangerously Genre Savvy, Master Xehanort and Padro Lodo would like him very much to keep his powers...so long as he doesn't betray Maleficent. He also has a very close..."friendship" with the Horned King due to both of them being former servants of the true darknes, the old ruler who became the Dark King due to Chernabog's influence.