Githyanki skull

The githyanki skull is the skull of a githyanki with an inlaid emerald that contains the trapped soul of a githyanki pirate.

Description
The githyanki skull resembles that of a human or elf, though with sharpened teeth and a longer cranium. Embedded in the right eye socket is a uncut emerald, kept there by a gold filigree.

The emerald contains the soul of a trapped githyanki pirate, which could be seen as a swirling shape that moved within the gem. When it wished to be seen, the spirit could show its face to those looking at the gem. The spirit can speak, both telepathically and aloud, to those around it.

The spirit claimed it had forgotten its identity, and that it would grant a Wish to a creature that destroys the gem, allowing it to pass on into the afterlife. This however was a lie, and doing so would instead free the trapped githyanki and trap the creature in its stead.

Background
At some point in time, apparently after Vecna was destroyed in the Age of Arcanum, a githyanki pirate was trapped within the emerald, which was set into a githyanki skull. This skull traded hands until it came into the possession of a collector, who displayed the skull in a private show room in his home, which was previously inhabited by General Krieg.

Campaign 1: Vox Machina
In Duscar of 810 PD, Vox Machina found the skull in the abandoned home while investigating/robbing it for Dr. Dranzel. Percy briefly touched the skull, turning it to face the wall on the belief that it may be a magical sentry. Pike cast Detect Evil and Good on the skull, and determined it to have a "immoral" presence. On the party's way out of the house, Grog picked up the skull and the spirit spoke to him, attempting to convince him to take the skull out of the house. Bolting out of the house, Grog explained to the Vox Machina that the skull claimed it could grant a Wish to anyone that would destroy it to free the spirit. Unsure of the entity's intentions, party took the skull back to Greyskull Keep and hid it within Percy's workshop.

The next day, the Chroma Conclave attacked the city of Emon. Grog attempted to convince the Percy to use the skull's Wish to defeat the dragons and undo the attack. Percy conversed with the skull and both he and Vax determined that there were too many risks to use the skull without having it properly Identified. Vex took the skull and asked if the spirit was Vecna, who responded that it was not. Grog became agitated and attempted to seize and destroy the skull, fighting Percy, Vex, and Vax to do so, but was unsuccessful. Allura Vysoren arrived at the keep and was able to Identify the skull and confirmed that would be unwise to trust it. As Allura left, Vex secretly gave the skull to her for safekeeping.