Wight

In the land of Graefsher, the unburied dead often get up and begin hunting the living. They call these animated creatures Wights: violent, malevolent constructs that lack clear sentience but are able to mimic basic body language and mannerisms to lure their prey closer. As they kill, they drain the lives from their victims to better kill again: they grow fangs in their rotting mouths, they can magically form claws when needed, and may develop other killing tools. 
None in Graefsher know exactly why these creatures rise from the dead. Many assume it is a curse placed upon the land. Others assume it is the touch of invisible spirits or the spell of a powerful necromancer. Certainly, the mistreatment of the dead is to blame in some way - a body left unburied, untreated, not even cremated, is a clear moral transgression that invites misfortune. This observation does hint at the truth, though morality has little to do with it. 
The Darzan University has recently discovered the Wights seem to be animated by Wight Worms: miniscule creatures, often invisible to the naked eye, that normally act as parasites on flies. When flies lay their eggs in a once-sapient corpse, wight worms also deposit their own larvae. These larvae activate the animation process as they quickly mature and reproduce themselves. Wight Worms reproduce in the Wight and begin infecting flies that land on the undead creature. Wight Worms also often deposit their microscopic young through the Wight's bite: creating a new host to produce more worms and attract more flies. Wight Worm eggs deposited by a Wight bite can only survive in dead flesh and represent no health threat to a living body.
These Wight Worms are Irradiated creatures that seem to be carefully attuned to Graefsher's unique regional ecosystem. While wight worms can exist outside of Graefsher, they seem to direct flies to stay for the most part - and their abilities seem to weaken generationally beyond their preferred place. Whether this is a magical connection or an ecological one is currently unclear.
While the primary functions and cycles of Wight Worms are ecological, there is a magical element at play: they do seem to absorb energy from the people they kill, allowing them to enhance and preserve their current host. This 'life siphoning' ability is confirmed to at least require a base level of ambient Ederstone radiation: outside of Stildane, the magical siphoning does not seem to occur.
While the Darzan University knows the current nature of Wights, this knowledge is basically unknown in the lands they haunt. This isn't the University keeping secrets necessarily, they just have no incentive to share their knowledge on the matter.