Phylactery

A phylactery is a vessel created though an arcane ritual to bind the soul of a powerful wizard or dragon from traveling to the Outer Planes after its death. A humanoid who undergoes this ritual is called a lich; a dragon is called a dracolich. The lich may only be permanently destroyed if its phylactery no longer exists to reform its body after death.

Appearance
Zathkira's phylactery, throbbing with a heartbeat, looked like a glass tube containing a faint blue energy.

Properties
After a lich bound to a phylactery is reduced to zero hit points, it gains a new body within two weeks, appearing within five feet of its phylactery and regaining all its hit points. A lich must periodically feed souls to its phylactery to sustain the magic preserving its body and consciousness.

A lich who fails to regularly feed souls to its phylactery fades into a demilich, decaying until only its skull remains. A demilich can reclaim its former power by feeding just one soul to its phylactery.

A group of competent mages or cultists can perform a ritual to transfer the soul of a dragon into a special gemstone that functions like a lich's phylactery. During the ritual, the dragon consumes a toxic brew that kills it instantly; its flesh rots away and the spirit inside the gem returns to animate the dragon's bones in dracolich form.

Vox Machina Origins Series II
In 809 PD, a dying mage named Drath Mephruhn, as a part of his ambition to reach lichdom, magically compelled Grog to travel into his lair within Gatshadow Mountain. Before Vox Machina was able to slay the mage, Drath managed to complete the ritual and embed his phylactery into Grog's chest.

Seeking the cure for Grog's necromantic infection, Vox Machina found a friend in Archmage Eskil Ryndarien, who agreed to aid them but required the necessary materials for the ritual: the skull of a Nightmare and the Heart of a nymph. He also confirmed that Drath had indeed became a lich who would be reborn within Grog in two weeks if the phylactery was not removed in time.

After fighting the Nightmare of the Umbra Hills and receiving a heart from Nahla, Vox Machina returned to Westruun, where the Eskil performed the ritual that destroyed the phylactery, but left lingering necromancy branded within Grog.

A long time ago, the dark mage Zathkira was struck down by Shiona, but preserved his soul in a phylactery within the subterranean caverns of the Plumgroves. Years afterward, following the trail of the forest's corruption, Capo destroyed his phylactery, slaying Zathkira.

Critical Role: Tal'Dorei Campaign Setting and Tal'Dorei Campaign Setting Reborn
As a part of the Skull of Udah adventure hook, Udah, a lich of tremendous power inhabiting the Tomb of Udah in the Dreamseep Marshlands, feeds the souls of all who die within the Dreamseep to its phylactery. His disembodied spirit controls the dungeon itself, and only retreats into the skull when it is in danger.

Explorer's Guide to Wildemount
As a part of the Evil, Arise adventure hook based in 835 PD, a powerful artifact of the long-deceased Archmage Oleyahs has been recovered from the ruins of Molaesmyr and transferred in Bysaes Tyl. Investigating the object to understand the destruction of the ancient elven city, researchers revealed it was the phylactery of Oleyahs, the archmage demilich.

As a part of the Bones of Frigid Doom adventure hook based in 835 PD, a death knight named Pentrakath attempts to stitch together a phylactery powerful enough to resurrect Vorugal as an ancient white dracolich, fueling it with the souls of hundreds of dead dragonborn in the Dreemoth Ravine.