Pact of the Lich King

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.

Expanded Spell List

You have access to the sorcerer spell list. 

Bond of life

At 1st level, you can use a bonus action on your turn to create a bond between yourself and a willing creature. The bond lasts for 8 hours, and for the duration you can use a bonus action on each of your turns to siphon a number of hit points equal to 2 + your warlock level from the creature, as long as this can’t reduce the creature to 0 hit points. Once the bond expires, you can’t use it again until you complete a short or long rest.

Shepherd of Lost Souls

When you kill a creature, you can choose to have
it rise 1 minute later as a zombie or skeleton under your control, unless it is
restored to life or its body is destroyed. The total CR of the undead under your control cannot exceed half your warlock level (rounded down) your warlock class level. If you make an undead and exceed this limit an amount of your other zombies under your control will become inanimate until total CR equals your class level.

When raising a non-humanoid this way use the template found for skeletons and zombies found in the Dark Arts Player's Companion.

Undead Thralls

Starting at 6th level,

Whenever you create an undead, it has additional benefits:

The creature’s hit point maximum is increased by an amount equal to your warlock level.
The creature adds your proficiency bonus to its weapon damage rolls.

Death Burst

By 10th level, your body has taken on the attributes of undeath. You have resistance to necrotic damage, and you age at a slower rate. For every 10 years that pass, your body ages only 1 year. When an undead under your control is reduced to 0 hit points it explodes in a burst of necrotic energy. Each creature within 5 feet of the undead must make a dexterity saving throw against your spell save DC, taking (4d8) Necrotic damage on a failed save or half as much on a success.

Shared Fate

At 14th level, you can bind yourself to another creature with negative energy. As an action, choose a creature within 30 feet of you. It must make a Wisdom saving throw against your warlock spell save DC. On a failed save, the target’s life becomes tethered with your own. Whenever you take damage within the next minute, the tethered creature takes the same amount of damage as necrotic damage. At the start of each of its turns, the creature can repeat the saving throw, ending the effect on a success. You must finish a short or long rest before you can use this feature again.