Orthax

Orthax is a powerful shadow demon who makes pacts of vengeance with mortals in exchange for souls.

In both Critical Role and The Legend of Vox Machina, Orthax is played by Matthew Mercer.

Appearance
When Orthax manifested before Vox Machina, its black smoke coalesced into a humanoid form that continued to grow until it reached the roof of the twelve-foot-tall tunnel they were in. Its bird-like beak is the inspiration behind Percival's mask.

Background
Orthax appeared to Percy, in what he thought was a dream, and offered him vengeance against those who destroyed his family. It was with Orthax's inspiration that Percy designed his first gun.

While on the hunt for the Briarwoods, Percy began to act increasingly more erratic and violent due to Orthax's influence. Dark smoke began to emerge from Percy's body and envelop him during these moments.

When Percy tried to sever his ties to Orthax, it appeared and fought Vox Machina. As a precaution, Scanlan threw Percy's pepperbox 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, and assisted her in the fight against Vox Machina on Glintshore, which led to Percy's death at the hands of Ripley. Vox Machina was able to fell the demon, however.

Even after being defeated, Orthax remained in the Material Plane through its attachment to Ripley's pepperbox, Animus. It used this attachment to grab hold of Percy's soul, preventing his resurrection until Keyleth managed to sever the thread connecting it to Animus through the use of Greater Restoration.

Percival de Rolo
Orthax made a pact with Percy after his family was slaughtered by the Briarwoods. Orthax offered inspiration for Percy in designing his deadly firearms; in return, every target that Percy killed in revenge was offered as a soul to Orthax. Percy eventually bucked the deal and expelled Orthax, with some help from Scanlan.

Anna Ripley
After being rejected by Percy, Orthax sought out one of his former revenge targets, Anna Ripley, who had been trying to create firearms of her own after Percy's design. Orthax offered the same pact to Ripley as it had to Percy, and she accepted.

The List
Each person Orthax made a pact with kept a list of people who had wronged them. Every time one of the people on this list was killed, that victim's soul was taken by Orthax to consume.

Abilities:
The following is drawn from the Monster Manual:
 * Senses: Darkvision.
 * Damage Resistances: Thunder, acid, fire, necrotic, and nonmagical physical weapons
 * Damage Immunities: Lightning, cold, and poison damage
 * Condition Immunities: prone, restrained, grappled, paralyzed, exhaustion, petrified, and poisoned
 * Vulnerabilities: Radiant damage
 * Light Sensitivity: Orthax has a lower AC as well as disadvantage on Perception and attack rolls while in bright light.
 * Incorporeal Movement: Orthax can move through solid matter.
 * Orthax can teleport from one shadow to another within a certain distance without using his movement.
 * Mark of Vengeance: Grants advantage on attacks against the marked creature. The Mark can be moved to another creature as a bonus action.
 * Rampage Pulse: (Recharges based on a die roll) Creatures within 20 feet of Orthax who fail a Wisdom saving throw (DC 17) immediately attack a nearby creature, even if it's an ally; on a success they take psychic damage.
 * Spells:
 * Dimension Door
 * Shadowy Escape: When Orthax is reduced to zero hit points, he becomes a small pile of shadow and attempts to return to his host.

Action:
 * Claw: (10-foot reach) Orthax's claws rake through the target's corporeal form, dealing 2d8 (plus an unknown modifier) of psychic damage. Orthax deals 2d8 extra psychic damage when he attacks with advantage.
 * Multiattack: Orthax makes three claw attacks.
 * "Grasp an element of your willpower": (Triggered in the course of a multiattack) On a failed Wisdom saving throw, Orthax does something that presumably dominates the target.

Appearances and mentions

 * Campaign One: Vox Machina


 * The Legend of Vox Machina

Trivia

 * When Taliesin created Percy's backstory, he left it up to Matt to decide whether Percy's dream vision of a smoky entity was real or just a dream. The appearance of Orthax in the story was as much of a surprise to him as the rest of the players.
 * Interestingly, Orthax is a shadow demon but is able to create pacts with at least two people (Percy and Anna). Fiends with the ability and propensity to create pacts or contracts are almost always in the domain of the lawful evil devils of the Nine Hells which are, in traditional D&D lore, in eternal conflict with the chaotic evil demons of the Abyss. Orthax being a shadow demon belongs to the latter.