The Decay is a dangerous force known throughout Niwen. It first appears after the Spirit Willow's passing and its light scatter across the land. It is like a plague that infects those who stay too long in the Silent Woods. Any creature who lingers too long in an area that is lifeless and decayed will essentially have their energy and life drained from them and die/turn into skeletal stones as in the case with the owls. Shriek somehow merged with the Decay at birth, which not only warped her appearance but also warped her strength.
Effects on Niwen
While the Silent woods serves as the most devasted area of Niwen and displays the most deadly effect the Decay has on the ancient forest, other areas within Niwen has displayed different ways the Decay affects the Forest.
Mouldwood Depths - because of the Decay, the darkness within the spider den has become lethal to anyone unfortunate enough to be engulfed in it.
Baur's Reach - After the decay arrived, an endless winter replaced spring.