Monster Name: Skeletal Rogue
Skeletons no longer require flesh or essence, but their drive to kill has been instilled over many stages of progressive decay. As a result, they will attack anything that approaches them, but they won't attempt to consume it after it is slain. The essence that animates them is energy at its most basic level, as the skeleton has lost all measure of will, intelligence, or personality. If not killed, a skeleton may eventually grind itself into bone dust, or its essence may finally evaporate into the ether.
Skeletal savants are the remains of warriors, wizards, and other adventurous types. They are similar in overall properties to other skeletons, but they are more capable in combat and often retain rudimentary skills from their adventuring lives.
Death guards are an aberrant form of these skeletons, as they are skilled, powerful, and intelligent. When fampyrs wish to avoid the gradual decay associated with their condition, they can engage in a risky, expensive, and extremely painful process that separates the tissues from bone and leaves a perfectly aware skeleton. In this case, essence does not decay in the flesh, and it instead resides in bone, a much hardier substance. Since the newly created death guard requires virtually nothing to survive and will not naturally decay further, it can "live" until it is killed.