Lots of good feedback on the Grey King, but one note that came up in discussion revealed a problem with the writeup. Most of the warlock patrons are more generalized as concepts, with the (curiously unspoken) assumption that the player will provide the name and details of the arrangement. So, if a Warlock’s patron is an archfiend, there’s an expectation that the player will identify the fiend, so there’s some implicit complexity, as the warlocks of Asmodeus may not see eye to eye with the warlocks of Orcus.

The fact that this assumption goes unspoken is actually a little bit of a hassle. If you’re already steeped in D&D lore (or Lovecraft) then you’ve probably got the resources to come up with a named patron off the top of your head. But if you’re fresh to the game then you might not even realize you should name your patron, much less have any sense of who the patron should be.

So, with that context, I declare the Grey King to be one of the Lords of Nothing, beings who exist at the end of everything. There are others – The Sleeping Queen, The Maw, The Last Trumpeter – and their agendas are virtually incomprehensible, but their interest in the unended universe gives them reason to recruit agents.
—
Cam Banks also reminded me of one of the coolest types of warlock patrons – vestiges. Unlike other categories, these are not a unified group in any way save type. They are what is left of a god after it dies, is cast down or otherwise is knocked from its place in the heavens. It might also include beings of power striving for divinity, proto-deities who can grant power in return for the sort of services that may help them ascend.

I love this idea. It’s flexible and powerful and usable in a variety of ways in a variety of settings. Some might have one or two cast out gods, some setting may be littered with the corpses of gods.

So with that in mind:

Vestiges

Even gods are not forever. Some of the once mighty have fallen from their places in the heavens, but can still offer power to those who seek it out. Some are ambitious powers seeking godhood, offering power in return for service. They are the dregs and prices that surround the divine, and they are collectively known as Vestiges. Some warlocks who seek vestige pacts view themselves as priests, while others take much more cynical perspective on the whole nature of gods and their relationship with their worshippers.

Sample Vestiges

• Elara, Fomorian Goddess of Beauty
• Fistandantalus, Ambitious Demi-Lich
• Antarchus the Dragon King
• Sel, the Sleeper in the Moon

Vestige Expanded Spell List

The extended spell list for a vestige warlock depends upon the semi-divine nature of the patron. Each patron has a domain, identical to the domains of Clerics (see the PHB). The vestige warlock’s expanded spell list is identical to the domain spell list for that domain.

Bonus Proficiency

Vestige warlocks gain proficiency with Knowledge(religion).

Bonus Cantrip

Vestige Warlocks gain access to the Thaumatury Cantrip if it is not already known.

Eldritch Smite

Starting at 6th level, when the warlock hits an enemy with a melee weapon or cantrip attack, you can expend one Warlock spell slot to deal additional psychic damage based on the slot level. It starts at 1d8 at level 1 and increases by 1d8 per slot level.

Tainted Mantle

Starting at 10th level, you may wrap yourself in an aura of eldritch energy that has the trappings of the divine and provides a degree of protection. The Warlock may take an action to summon the mantle, which grants 3d6 temporary hit points.

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

Dead God’s Mark

Starting at 14th level, the warlock may take an action to inscribe a symbol of the patron. This has the effect of the 7th level spell of the same name, but the warlock may use only one type of symbol, selected when this ability is gained.

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