Orthax

Orthax is a shadow demon who makes vengeance pacts. As an NPC, it is played by Matthew Mercer.

It appeared to Percy, in what he thought was a dream, and offered him vengeance against those who destroyed his family. While on the hunt for the Briarwoods, Percy began to act increasingly more erratic and violent due to Orthax's influence. During several fights, Orthax shrouded Percy in smoke.

When Percy tried to sever his ties to Orthax, it appeared and fought Vox Machina. As a precaution, Scanlan threw Percy's pistol into acid, in hopes that that would sever its tie to him.

Orthax reappeared when Vox Machina caught up to Anna Ripley, as she had made a similar pact with it. They were able to fell it but as a demon it is likely to reform in the Abyss and return.