Warlock Patron: The Pale Stranger
Your patron is beyond death, an unliving monstrosity more powerful than majority of petty undeads you might meet in your travels. An archlich, a ghost of a dead god, a progenitor of vampires, the first ghoul, a monarch who sacrificed whole kingdom for life-in-death. It could be any of those.
What are its goals? Gathering greater power in death? Extinguishing life across the world and spreading undeath? Reversing its transformation and returning to life? Going further and becoming a true god? Seeking eternal rest for itself?
Expanded Spell List
1st—inflict wounds, ray of sickness
2nd—gentle repose, see invisibility
3rd—feign death, revivify
4th—death ward (1 hour duration),
5th—contagion, destructive wave (necrotic damage)
At 1st level, you gain affinity for death. Whenever a living creature drops to 0 hit points or is killed within 60 feet of you with a clear path to you, you immediately sense it, and can spend one of your warlock's hit dice to regain hit points as a reaction. You can use this ability even when you are dying. If multiple creatures are dropped to 0 hit points or killed by the same attack or effect, you can spend one hit die per creature. Creatures with 0 CR are too weak to trigger this ability.
At 6th level, you gain ability to cast animate dead once without using components. At 8th level, and every two levels thereafter, you can animate or maintain control over two more skeletons or zombies. After you used this ability you need to finish a long rest to use it again.
At 10th level, you become immune to diseases and frightened conditions, and gain necrotic resistance.
At 14th level, undeads you control add your Charisma bonus to their attack and damage rolls. When you create an undead, it adds your Charisma bonus to its hit points, and it has AC of 10+you Charisma bonus or its normal AC, whichever is higher.