Elder Lich.
A type of undead that has evolved from the normal undead or skeleton depending on which type they are as they both can ascend to either of them. If an undead or a skeleton gets to reach a certain level by killing humans and other creatures, they have the chances to evolve into a normal lich, that's when they gain various abilities that they can utilize to complete their evolution and progress further and those that became successful in doing so evolves into an Elder Lich where their abilities amplified and depending on how strong they are from being a normal lich, they might become a very dangerous being that some would even become a boss of their own dungeons.
