When Vader warned Luke that he underestimated the power of the Dark Side, he was not joking. As the Ring slowly corrupted Frodo, it had visible and mental effects on him. As clerics fail to uphold the ideals of their god, their patrons turn away.
This short set of rules introduces the Shadow Track - a way of tracking Light and Dark points. As characters ascend into the light or descend into the darkness, they gain manifestations.