Warlock - The Archlich

You have made a pact with an archlich, a creature that has existed since the dawn of the last age and holds secrets of arcane magic that have been forgotten for thousands of years. Such a being desires only to expand its own power and influence, only using you as a pawn in its far larger scheme. Any lich powerful enough to form a pact has lived for many thousands of years, and many of them were involved in the invention of lichdom itself.

Soulkeeper

Starting at 1st level, you can force the souls of the dead to protect you from attack. Whenever a creature within 60 feet of you is reduced to 0 hit points, you can use your reaction to temporarily
tether its soul to your body. Until you lose your concentration (as if you were concentrating on a spell), your AC equals 12 + your Charisma modifier + your Dexterity modifier if you aren’t wielding a shield. If you lose your concentration, the soul goes free and the bonus is lost.

Phylactery Ring

Starting at 6th level, your patron grants you a magical ring that can serve to revive you from death. If you would be reduced to 0 hit points while you a have a soul tethered to you with your
soulkeeper feature, the soul is first bound the ring, empowering it, before you fall unconscious. If you die while wearing the empowered ring, you are revived 24 hours later with 1 hit point, your body fully restored at the location of the ring. If you instead get up from unconsciousness, the soul is removed from the ring and re-tethers to your body.

If you ever lose the ring, you can request your patron to grant you a replacement during a long rest.

Undying Flesh

By 10th level, your body has taken on the attributes of undeath. You have resistance to necrotic damage, gain proficiency in Constitution saving throws, and you age at a slower rate. For
every 10 years that pass, your body ages only 1 year.

Souleater

Starting at 14th level, you can consume the souls you’ve enslaved to heal yourself. When you lose concentration on your soulkeeper feature, you can choose to consume the soul, rather than freeing
it. If you do so, you regain hit points equal to half your hit point maximum, and each creature of your choice within 10 feet of you becomes frightened of you until the end of your next turn.

Once you use this feature, you can’t use it again until you finish a long rest.