From NexusClash Wiki
The Pariah is, in the most simple terms, a corrupted soul. In more elaborate terms, a Pariah is a soul who has allowed itself to become consumed by hatred, and have had their soul twisted and warped as a result. When a soul becomes twisted enough, it becomes a creature as deformed on the outside as it is on the inside. The perversion of the body seeps all the way to their blood; a wounded Pariah is forced to seek their own means of tending to themselves (such is the life of an outcast). However, these discarded souls frequently band together, united against those who shun them. Unlike the Defiler, a Pariah will seek to turn their curse into a strength, drawing power from a combination of their deformities and lust for vengeance.
Being a demon, a Pariah cannot accept external healing. They are able to heal themselves, however.