Wreath of the Prism

The Wreath of the Prism is one of the Vestiges of Divergence. This loop of golden thorns is inset with dozens of gems representing the five colors of Tiamat. It is currently in the possession of Arkhan the Cruel.

Dormant state

 * You have darkvision out to a range of 60 feet. If you already have darkvision, wearing the wreath increases the range of your darkvision by 60 feet.
 * When you hit a beast, dragon, or monstrosity of challenge rating 5 or lower with an attack, or when you grapple it, you can use the wreath to cast dominate monster on the creature (save DC 13). On a successful save, the target is immune to the power of the wreath for 24 hours. On a failure, a shimmering, golden image of the wreath appears as a collar around the target’s neck or as a crown on its head (your choice) until it is no longer charmed by the spell. If you use the wreath to charm a second creature, the first spell immediately ends. When the spell ends, the target knows it was charmed by you.

Awakened state

 * You can affect creatures of challenge rating 10 or lower with the wreath.
 * The save DC of the wreath’s spell increases to 15.

Exalted state

 * You can affect creatures of challenge rating 15 or lower with the wreath.
 * The save DC of the wreath’s spell increases to 17.

CelebriD&D with Joe Manganiello
The Wreath of the Prism was kept in the Vault of Shumas in the Aggrad Mountains. Tiamat sent visions of the artifact to Arkhan in his dreams, so he spent months of frustrating research seeking it out until finally coming across a monk of the Cobalt Soul named Duan who had the knowledge he needed. He hired a group of mercenaries—Keyleth, Percival de Rolo, the Headmistress, and Dupont Dupont—to help him delve into the Vault. Arkhan barely took control of the undead caregiver there, and commanded her to show him to the artifact. She brought forth a manticore, who (following the caregiver's lead) willingly relinquished the Wreath on its neck. When Arkhan put the loop around his own neck, the thorns suddenly jutted deep into his neck and dealt him piercing damage, changed the appearance of his eyes, and changed his vision so that colors were more vibrant and he could see the heat of others' bodies. He then was able to command the manticore.

When Vox Machina encountered Arkhan in Thar Amphala, he was attempting to grapple a gloomstalker to dominate it with the Wreath of the Prism, and he eventually succeeded. His eyes flared yellow when he commanded the creature with it.