During the Mortal War both sides fought with all the strength they could muster. During the final confrontation both Brenna and Machiavelli fell. While the armies were distracted by each other, Machiavelli was betrayed by one of his spawn.
Sheridan under the control of Reaver sought to kill his master to bring death to the mortal world. While many thought that this was, also what Machiavelli wanted, that was not the case. He wanted a world in which the undead ruled over the living. World of night, for he understood that a world with nothing living in it would quickly fade away.
This sparked his to mix his own life energy with Brenna’s. Having thousands of years to study magic gave him the knowledge he needed to create a curse that would drive the living and undead farther apart, to prevent Reaver’s plan from coming to fruition. What he failed to factor in, was the energy and life force of the earth itself.
Now the world herself is fighting back. She has decided to take back what is hers. A mist that started the day of the final battle, covers the ground and continues to rise. This mist takes any organic material and transforms it. This transformation comes in many ways. Plants fight back, in ways they weren’t able to in the past. Those who Terra calls to her defense, Druids, Rangers and their like, know little of why their often benevolent mistress has chosen now to rise up, and without mercy, strike down mortal kind.