The Underworld carries its own potent Resonance: the energy of death itself. Mages who dabble too much in such studies can be afflicted with Jhor, the Resonance of death energy. Jhor can be considered as a form of Quiet, albeit one that affects death mages instead of the Marauders.
Normally, souls discharge that energy in the cycle of death, but such an accumulation is unhealthy and unbalancing in the living. Mages who work with Entropic energy, who dabble in necromancy and death, often accumulate Jhor. Tradition mages who enter the Underworld too frequently, who spent too much time studying the deadlands, or who associate too much with death tend to develop Jhor. The Euthanatos in particular have learned to recognize this particular malady due to their long association with the deadlands, and they can often help mages in the early stages to achieve a better level of balance. This Tradition is also the one most affected by Jhor and as a result, they are extremely vigilant in their detection of its symptoms in themselves and others.
The mage assumes a pallid visage and an obsession with death. The mage's normal moral inhibitions fall away in favor of a desire to associate with and understand death energy. In actuality, the mage becomes fixated on the return to primordialism, but the living mind and body can't handle this reunification. As a result, the mage slides into a study of necromancy and draws away from other living beings, becoming gaunt and sociopathic, eventually degenerating into little more than a magical killer. Most of them, sooner or later, try to bring down the Shroud.