Lich

A lich is a powerful wizard or dragon who has been preserved as an undead through a powerful ritual that trapped its soul in a vessel called a phylactery. A dragon who undergoes this ritual this is called a dracolich. A lich who fails to regularly feed souls to its phylactery fades into a demilich.

Appearance
Liches are typically near-skeletal in appearance. Vecna, in his recently revived form, appeared as a gaunt husk of a man wearing long tattered red, purple, and black robes. His skin was weathered and decayed, pulled taut against his skeletal frame; there was no hair on his spotted head. His cheeks were sunken around skeletal teeth in a terrible grin.

If a lich degrades into a demilich, what remains of its body disintegrates and only its skull remains.

When a dragon becomes a dracolich, its flesh draws taut against its skeletal frame or is shedded, and its eyes are replaced with floating points of light.

Abilities
All of the following is taken from the Monster Manual, 5th Edition, and may not be exactly canon for Critical Role, as no lich, demilich, or dracolich has been fought onstream.

Lich abilities

 * Spellcasting: The typical lich is an 18th-level wizard who keeps prepared many damaging spells and several spells for protection and escape.
 * Paralyzing Touch: A melee spell attack that damages and paralyzes the target creature for 1 minute unless and until it makes a Constitution saving throw.
 * Damage Resistances: cold, lightning, necrotic
 * Damage Immunities: poison, bludgeoning/piercing/slashing from nonmagical attacks
 * Condition Immunities: does not take points of exhaustion, can't be charmed, frightened, paralyzed, or poisoned
 * Turn Resistance: Advantage on saving throws against effects that turn undead.
 * Rejuvenation: A destroyed lich whose phylactery is intact will gain a new body next to the phylactery sometime in the next 10 days.
 * Legendary actions (3/round)
 * Cast a cantrip
 * Paralyzing Touch (2 actions)
 * Frightening Gaze (2 actions): The target becomes frightened unless and until it makes a Wisdom saving throw.
 * Disrupt Life (3 actions): All non-undead nearby take necrotic damage, with half damage on a successful Constitution save.
 * Lair actions (can't use the same action two rounds in a row)
 * The lich regains a spell slot of a random level below 9th-level.
 * A target creature is connected to the lich by a cord of negative energy; for the next round, whenever the lich takes damage, the target creature must make a Constitution saving throw or take half of the damage that would have been done to the lich.
 * The lich commands the spirits of creatures who have died in the lair to attack a target, dealing massive necrotic damage, or half damage with a successful Constitution saving throw.

Demilich abilities

 * Damage immunities: necrotic, poison, psychic; bludgeoning/piercing/slashing from nonmagical attacks
 * Damage resistances: bludgeoning/piercing/slashing from magic weapons
 * Avoidance: When making a saving throw that normally allows the target to take half-damage, a demilich takes no damage on a successful save and half damage on a failed save.
 * Turn Immunity: Immune to effects that turn undead.
 * Condition immunities: Immune to exhaustion and being charmed, deafened, frightened, paralyzed, petrified, poisoned, prone, or stunned.
 * Howl: All nearby creatures who can hear the howl make a Constitution saving throw, becoming frightened on a success or dropping to 0 hit points on a failure.
 * Life Drain: Up to three creatures the demilich can see very nearby make a Constitution saving throw; on a failure, they take necrotic damage and the demilich regains an equivalent number of hit points.
 * Legendary actions (3/round)
 * Flight: Flies up to half its flying speed.
 * Cloud of Dust: Creatures very close become blinded unless they make a Constitution saving throw, in which case they become immune to this effect, until the end of the demilich's next turn.
 * Energy Drain (2 actions): All nearby creatures make a Constitution saving throw; on a failure, the creature's hit point maximum is reduced (a Greater Restoration ends the effect).
 * Vile Curse (3 actions): A target creature becomes cursed, with disadvantage on attack rolls and saving throws, unless and until it succeeds on a Wisdom saving throw.

Dracolich abilities
Upon becoming a dracolich, the creature loses the dragon creature type and becomes undead. In addition to all the abilities it had in life, a dracolich gains the following features:
 * Magic Resistance: Advantage on saving throws against magical spells and effects.
 * Condition Immunities: No longer takes points of exhaustion and can't be poisoned, paralyzed, frightened, or charmed.
 * Resistance to necrotic damage and immunity to poison damage.

Age of Arcanum
Guuthal the Ever-Fed was an ancient black dragon who used forbidden rituals to become a dracolich and terrorized the world during the Age of Arcanum.

A century before the Calamity, the archmage Vecna achieved lichdom, amassed followers and undead forces, and with them disappeared into the Shadowfell, where they conquered the city of Thar Amphala and there built a tower called Entropis that served as his base. From there Vecna exploited the celestial solstice, a merging of ley energies, that gave him the power to open portals at a whim, so that his forces could strike with precision and retreat to Thar Amphala before retaliating forces could muster. Thus he overcame some old enemies and forced them to bend the knee, at which time he slew them and raised them as undead to serve him. One such rival, Kas, was offered vampirism in exchange for fealty as a Vecna's chief lieutenant, and Kas accepted. Eventually, as Vecna was attempting a ritual to ascend to godhood, a holy army invaded Thar Amphala. When Vecna was winded from defending himself, Kas betrayed Vecna, and in their struggle all but the lich's eye and hand were destroyed.

One of Vecna's main laboratories on Exandria was in the Verstglade, where he performed countless experiments that left the forest corrupted and haunted by abominations of his creation. He was banished before he could unleash these creatures on Wildemount.

Vecna left instructions to his most devoted followers allowing for the possibility of his rebirth. He was later considered a lesser deity or "patron saint" of dark, coveted secrets, and this belief and worship lent him new power.

Campaign One: Vox Machina
Vecna's cult, the Remnants, conspired to bring back Vecna and help him achieve godhood. The Briarwoods were among his followers, and their takeover of Whitestone, which led to Percival de Rolo's origin as a vengeful hero, was part of a plot to siphon energy for this purpose.

One of Vox Machina's earliest adventures together was touched off by Drath Mephruhn, a dying mage who magically abducted Grog so as to implant his phylactery into the strong goliath's body, allowing him to take over the body when he became a lich. Though Drath's initial form was defeated, the phylactery began to have increasingly troubling effects on Grog, and Vox Machina had to obtain certain magical components so that Eskil Ryndarien could perform a ritual to safely remove the phylactery. Drath briefly became a lich with control of Grog's body just as the ritual was about to take place, but the party managed to restrain the dominated body until the ritual could be completed, and Drath's spirit was trapped inside the components and destroyed.

When Vox Machina was liberating Whitestone from the Briarwoods, they witnessed the creation of a ziggurat sphere for a purpose they didn't understand. Eventually, they discovered another ziggurat in Marquet, and upon investigation found that the ley energy was being siphoned to Thar Amphala. The party arrived in time to witness the return of Vecna, but Vecna and his allies soundly defeated Vox Machina, killing Vax'ildan in the process. The party scrambled for some means of stopping Vecna, enlisting the help of multiple gods while Vecna ascended to godhood himself. Vox Machina, with the help of some of their adventuring allies, were able to banish Vecna beyond the Divine Gate before he could fully come into his new power.

Critical Role: Tal'Dorei Campaign Setting
The description of the Dreamseep Marshlands is dominated by the presence of the Tomb of Udah. Udah the Undying, once a formidable lich, had by 812 PD faded into a demilich who still commanded undead minions within his vast necropolis.

While exploring the Ruins on Rumblecusp, the Mighty Nein encountered undead followers of the dracolich Oracs the Enduring; these servants had been displaced from Blightshore.

Explorer's Guide to Wildemount
In the epic-level adventure hook Bones of Frigid Doom, a death knight named Pentrakath attempts to raise the ancient white dragon Vorgual as a dracolich, using various artifacts and the stolen souls of hundreds of dead dragonborn.

Another epic-level adventure hook, Of Vaults and Vengeance, takes the adventurers through an encounter with Oracs the Enduring and his minions, including a core spawn seer.

Two epic-level encounters are offered that involve demiliches. One random encounter in Eiselcross starts with the discovery of a skull frozen in the ice of Eiselcross that turns out to be a demilich. Another adventure hook, Evil, Arise, involves the recovery of a relic of a fallen archmage of Molaesmyr that turns out to contain his demilich form, which proceeds to rain destruction on Bysaes Tyl.

Notable liches

 * Vecna, a lich from the Age of Arcanum who eventually ascended to godhood
 * Drath Mephruhn, a dying mage or shade who briefly achieved lichdom by placing a phylactery in Grog Strongjaw's chest
 * Udah the Undying, a demilich whose great tomb in the Dreamseep Marshlands has drawn in warriors from every era of Tal'Dorei's history, now serving Udah as undead minions
 * Oleyahs, an archmage of Molaesmyr who became a demilich
 * Guuthal the Ever-Fed, an ancient black dracolich who terrorized the world during the Age of Arcanum
 * Oracs the Enduring, an ancient black dracolich who commands undead and aberrant minions in the catacombs beneath Ghor Veles