Exposure to magical radiation can lead to loss of control. Loss of control is when a person loses cohesion and becomes and aberration/demon/undead through exposure to arcane radiation. The campaign is based around destroying things pushed beyond their limits.
Upon loss of control you convert into a creation/aberration/demon of the level of the check failed. There is no way to bring back someone who has converted. Created monstrosities are hunted and killed where that is possible.
In general all aberrations/demons/undead in the world are from out of control magic. Created monstrosities are uncontrolled and destructive. There is no sense of past self at creation time.
Creation levels
items converts to a creature based on their item level.
spells converts to caster-level +1d4.
Converted creatures are selected to be an appropriate type for the situation.