Skeletons are the resurrected bones of a creature. Bone magic is actually a type of unholy earth magic. This means that malevolent and extremely skilled earth magicians can make use of skeletons. While they may be made of earth, Skeletons’ main users are necromancers. Bone necromancers are an even more specific wielder of bone magic.
Skeletons may have shreds of flesh or not. Sometimes skeletons have eyeballs, sometimes empty sockets, other times some sort of glowing orb of magic within the sockets. Sometimes the hollow of the bones in skeletons are filled with some sort of material to make them tougher. Depending on the resurrector’s intent for the skeleton, they could be filled with anything from plague organs to gemstones.
It is usually a mystery as to how skeletons move with no tendons connecting the joints and no muscles to move them. Be sure to explain how your skeletons move when playing them. A few options are: they have tendons, they move by magic, their soul/spirit is moving the skeleton or they are being manipulated by an external source. Unless imbued with a specific set of instructions, skeletons are will-less. If left unattended skeletons will stand idle for all eternity until either the magic holding their bones together fades or their bones and possible tendons crumble. The only way a skeleton can act on it’s own is when possessed, bound to or infused with a spirit. Souls are too frail to control a skeleton fully.