The first encountered type of skeleton. They attack with melee, and are found within the medium levels in Brightstone, primarily.
The ranged variation of the skeleton knight. They attack with bows, and are found in the same levels as the skeleton knights.
The mage/cleric variation of the skeletons. They do not attack, however they constantly heal either themselves or other enemies on the battlefield. They also have the ability to teleport around the battlefield. However, due to a recent update, they now have a finite amount of mana.
Black Skeleton Knight:
The 'elite' variation of the skeleton knight, they deal more damage, have heavier armor and are found primarily in the middle - later levels of Doomvale. Two of them are also summoned by the Lich during the final boss fight.
Black Skeleton Archer:
The 'elite' Variation of the skeleton archer, they deal more damage and attack quicker, while having slightly more armor. They are found in the middle - later levels of Doomvale. Two Black Skeleton Archers are also summoned by the Lich during the final boss fight, simultaneously with the Black Skeleton Knights.
Black Skeleton Mage:
The 'elite' variation of the skeleton mage, they heal for more health with each cast, have a larger mana pool, and also teleport slightly more frequently. They are found primarily in the middle - later levels of Doomvale.
The Lich is the final boss encountered in the game, and is therefore the hardest to kill. He can be considered the 'boss' of the Skeletons. He is a mage type enemy, however does not heal himself nor does he teleport. He also summons 2 Black Skeleton Knights and 2 Black Skeleton Archers to aid him in battle.
All skeletons, excluding the Lich, are also encountered very frequently in Arena combat, where they often appear in groups of 4+ and are also sometimes joined by more during the fight. As the arena killcount gets higher, the Skeletons that appear become the Black variations of themselves, and then continue to grow stronger as the killcount is raised higher, as with all arena monsters.