Skeleton

Skeletons (スケルトン) are a type of undead beings that are effectively walking moving bones.

Background
Skeletons are undead summons brought forth by necromancers to serve them. Thus there exists several variant types, depending on how much power the caster invested in summoning.
 * Skeleton Warrior
 * Skeleton Mage
 * Skeletal Dragon
 * Elder Lich
 * Overlord
 * Bone Vulture

Appearance
Skeletons are magical reanimated bones of dead humans. They wear little or no armor, and typically wield low-level weapons, like a simple sword and a shield,.

Abilities
Skeletons possess an immunity to cold damage attacks. Skeletons prove to be relentless combatants, fighting without seemingly suffer from neither pain nor exhaustion.

Trivia

 * Guu and his troll minions made the assumption that Ainz was a skeleton. Ainz found it to be a rude association, as he was an Overlord, a distinct upper level undead.