Phylactery

A phylactery is a vessel created though an arcane ritual to bound a soul of the powerful wizard or dragon from traveling to the Outer Planes after its death. A humanoid who undergoes this ritual would be called a lich, a dragon would be called a dracolich. If the phylactery is destroyed, the life escapes the lich.

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

Properties
After a mage or lich bound to a phylactery reduced to zero hit points, it gains a new body within two weeks period, appearing within 5 feet of phylactery and regaining all 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 the skull marks its only remain. A demilich can reclaim its former power by feeding just one soul to its phylactery.

A group of compitent mages or cultists can perform a ritual, transfering a soul of a dragon to a special gemstone that functions like a lich's phylactery. During the ritual, the dragon consumes a toxic brew that slays 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 will be reborn within Grog in two weeks, if the phylactery would not be removed in time.

Fought Nightmare of Umbra Hills and receiving a heart from Nahla, Vox Machina returned to Westruun, where the Archmage performed the ritual that in time destroyed the phylactery, leaving a lingering necromancy branded within Grog.

Long time ago Zathkira, the dark mage was struck by Shiona, but preserved his soul in phylactery in the subterranean caverns of Plumgroves. Years after, following the trail of the forrest's corruption, Capo destroyed his phylactery, slaying Zathkira.

Explorer's Guide to Wildemount
As a part of 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. Invistegating the object, in hopes to understand the destruction the ancient elven city, researchers revealed the deceptive phylactery for Oleyahs, the archmage demilich.

As a part of 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 souls of hundreds of dead dragonborn in the Dreemoth Ravine.

Tal'Dorei Campaign Setting Reborn
As a part of Skull of Udah adventure hook based in 836 PD, 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.