The Laughing Hand

 was the Undying Chosen of The Crawling King: one of the god's most loyal and most powerful zealots. As an NPC, was played by Matthew Mercer.

Appearance
Wearing a deep brown, oily, black-stained hood and cloak, the Laughing Hand stands a full ten to twelve feet in height. His cloak hides much of his torso, dangling just past the forearms. Beneath the hood is a sagging open jaw, sharp broken teeth, and pale dirty skin weirdly twisted to look like some sort of horrifying mockery of a human face. He wears red stained leather across the body and legs, and heavy boots. His right hand is missing below the forearm, and where the hand would be is a long double-sided blade affixed and built into his arm.

Background
The creature known as 'The Laughing Hand' was once a warrior called Ganex who led an army against Torog, the Crawling King. When the army was defeated, Torog captured and tortured Ganex, twisting him into the Laughing Hand and cursing him to an endless cycle of servitude by trapping his heart in an extraplanar space. Many magical practitioners attempted to find his heart for their own research, and eventually a wizard, Halas, was successful.

The Laughing Hand is mentioned in this episode when his name is mentioned by the head of the Aasimar when Caduceus interrogates it.

Upon being freed from his sarcophagus by Obann, the Laughing Hand swiftly summons his shadow hounds and then attacks the Mighty Nein. The party manages to land a few blows on the champion of the Crawling King, but watch in horror as laughing mouths appear from the creature's wounds. After Fjord slays Obann, Obann in his dying breath tells Yasha to avenge him: she then seemingly switches allegiances and begins to aid the Laughing Hand by attacking her former friends and allies. Beau discovers how to seal the gate and the group rallies in a last ditch effort to retreat. As the Mighty Nein attempt to escape, Fjord is grappled and brought to the brink of death by the Laughing Hand, but is pulled to safety with the combined efforts of Beau and Caleb. Eventually the party are able to seal the tomb, trapping Yasha and the Laughing Hand inside. Sometime after, the Laughing Hand and Yasha break through the initial tomb door and begin to make their escape from the tomb.

While studying Yussa's map of the Heirloom Sphere, The Mighty Nein discover the Permaheart chamber. Beauregard remembers that the Laughing Hand's heart was hidden on another plane to ensure he could not be killed. She realizes that his heart could be located in the Permaheart chamber.

The Mighty Nein enter the chamber and destroy the Permaheart. They subsequently ask Allura Vysoren to scry on the Laughing Hand, and she reports back that the Hand was in terrible physical shape and being berated by another individual for falling apart "near the finish line," in reference to some event happening soon. The Mighty Nein guessed that the individual berating him was Obann.

Weakened by the destruction of the Permaheart, the Laughing Hand has lost his resistances and is a considerably weaker foe to the Mighty Nein in the battle in the cathedral of Pelor. After Beau stuns him, Caleb finally incinerates him with Web of Fire. The sound of laughing grows louder and louder, then thinner and thinner, until it dies out, leaving his standing, blackened body still on its feet in the Chantry.

Abilities
The Laughing Hand can use an action to summon three "shadow hounds" that have pack tactics and resistance to fire damage, and can traverse or climb difficult terrain without a movement penalty. The Hand can dismiss the hounds at will.

When the Laughing Hand is struck by piercing or slashing damage, mouths appear where the wounds were inflicted and add to the dissonant chorus of laughter. Creatures within 15 feet who can hear the laughter must make a Wisdom saving throw or become frightened and have their movement speed reduced to zero for one round. The laughs get louder as more piercing and slashing wounds are inflicted, apparently increasing the save DC.

Trivia

 * Since Obann refers to the Laughing Hand as a "zealot", it's possible that the Laughing Hand is also a Path of the Zealot Barbarian, like Yasha.