The Lich

Before his change, the Lich wore a crown. Another feature of his is his horns, one of which has broken off. However, before being struck down by Billy, both of his horns were intact, so it is possible that it got broken off as a result of that encounter. The Lich also dresses in a large, loose robe with multiple layers and a large cape that is severely torn at its end.

Physically, the Lich is also remarkably large. In the flashback in "His Hero", the Lich is shown to rival Billy in size. The arms of the Lich are bare-bones with little to no tissue left, and his skeletal hands burn with an eerie fire when casting spells. His face is defined by horrific green lights as pupils peering out of his empty eye sockets, and pale undead skin is pulled tight against his nose-less skull. His skin is frayed away from his lips revealing a wicked and perpetual grin.

The Lich is driven by a rather single-minded goal: to destroy all life. He appears to show little interest in anything that does not further his ambitions towards this dark end. He also has an apparent hatred for all living things, as Princess Bubblegum said that his only desire was to destroy life, and his wish to Prismo was "for the extinction of all life." It has been said that he brings sadness everywhere he goes.

Despite this, the Lich is not a mindless murdering psycho that just kills anything he sees, like most hostile monsters. He specifically wants to eradicate all life in existence and seems to understand that simply destroying everything in his immediate vicinity wherever he goes is not the best way to go about that. He instead is a deep planner; given his lack of aging, and lack of most emotions, he is more than happy waiting centuries for the exact right moment to do whatever is necessary in order to further his final goal of total extinction, no matter what he believes is the best course of action for that, even if it means making temporary allies to kill later.

He is viciously cunning and quick to learn from his mistakes. He methodically targets people and things that have proven a problem for him in the past by either destroying them outright such as in the case of the Gauntlet of the Hero or using them as pawns to further his own agenda in the case of Billy to manipulate Finn.

The Lich's most notable flaw is his arrogance and his single-minded nature. In each case, his defeat has been at the hands of opponents towards whom he was derisively dismissive.