Ghost

As an undead, the typical ghost is defined by its original species in its appearance. Unique to them is their ethereal, transparent nature, vague and ill-defined bodies, and unusual colorations. Indeed, many ghosts appear as gaseous apparitions, though some can resemble water or fire in both color and appearance.

Intangible – They have no corporeal form, and so mundane materials have almost no affect against them. Magical attacks and mana-infused objects are necessary to interact with their purely mana-comprised existence.   Undead Endurance – Driven by their metabolized mana, they can keep going for absurd amounts of time. In fact, the only time they stop is when they've lost all their mana, or lost track of their prey.   Life Sense – They can sense the presence of the living in a supernatural manner. This means despite loss of critical sensory organs, like eyes or ears, they can still track their targets with disturbing precision.

Manavore

Ghosts arise when the strong, negative emotions (hatred, trauma, etc) provoke the dead awake. Lacking a body, for one reason or another, all their mana goes into constituting an intangible form, vaguely resembling whoever they were in life. Contrary to popular belief, not all ghost types can fly, and many prowl around on the ground, unhindered by terrain or things in their way.   As is typical with all undead, their reanimation is driven by their strong emotions, and much of their memories fade away or become indistinct. Only the strongest of impulses compel ghosts, be it love of something like a child or spouse, or the hatred of being betrayed, or tortured and left for dead. Regardless, they are trapped in their wretched state, and their malformed awareness goes increasingly insane the longer they remain. The oldest ghosts have no resemblance at all anymore, simply hateful spirits who exist to continue their own selves however they can.   For the most part, their intangible nature means one needs special tools to take care of them. Magical attacks, and mana-infused objects, are the most literally effective tools against them. Psychological manipulation of still-reasonable ghosts can, in a sense, lead to their pacification and ultimate dismissal. Some are even impacted by religious iconography, especially of faiths they know of (if not practiced) when in life. This makes the task of ghost hunting a rather complicated one, as much research can be needed to effectively understand, then remove, the ghost.   Most just go for the magic spell or sword route.   Ghosts are chiefly sustained on ambient mana, or the emotions of the living who become distressed by them. This can mean some areas are haunted for literal centuries, while some are plagued because a ghost has targeted a family. Without a continual stream of a nearby source, ghosts quickly evaporate, and so they are even more constrained to locations than skeletons are.