Ebon Serpent Patron

Individuals who subscribe to the belief in the end of days eventually become consumed by their obsession with its inevitability, often envisioning it taking the form of an ebon serpent that roams the multiverse. Those who seek power from this serpent gain profound insight into impending events. They regard the world and its inhabitants as temporary entities destined to perish. Their knowledge reveals to them the weakness of other creatures, information which they exploit to further their cause. They exude confidence in their knowledge, using it to alter reality toward an eventual doom. They are usually fanatical individuals with esoteric manners and dark secrets.

From Torrents of the Spellhoarder by Elderbrain.com

Level 1: Ebon Serpent Expanded Spells

At 1st level, your Ebon Serpent patron lets you choose from an expanded list of spells when you learn a warlock spell. The following spells are added to the warlock spell list for you.

Archfey Expanded Spells

Spell Level	Spells
1st	bane, detect evil and good
2nd	augury, detect thoughts
3rd	bestow curse, clairvoyance
4th	death ward, divination
5th	commune, geas

Level 1: Dark Devotion

Starting at 1st level, your conviction in the forthcoming apocalypse strengthens your self-awareness. You gain advantage on saving throws against the Charmed condition.

Level 1: Know Vulnerability

Starting at 1st level, you gain the ability to pinpoint the weakest spot on any given creature. As a bonus action, you can gain knowledge of the lowest ability score of a target creature you can see, as well as its vulnerabilities.

At 6th level, you also gain knowledge of all of its condition immunities.

At 10th level, you also gain knowledge of all of its damage resistances and damage immunities.

Level 6: Conviction of the Spared

Starting at 6th level, you know when your own end will come. You can reroll a failed saving throw. Once you use this feature, you can’t use it until you finish a long rest.

Level 10: Exploit Weakness

Starting at 10th level, you learn how to bring about an almost certain doom upon a creature. You can use your reaction to target a creature that is about to make a saving throw. The target creature makes its saving throw with the ability of your choice instead of the ability in the original saving throw.

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

Level 14: Invoke the End

Starting at 14th level, you can make any creature face its ultimate demise. As an action, you can target a creature that must make a Charisma saving throw (DC equals 8 + your proficiency bonus + your Charisma modifier). On a failed save, the creature is reduced to 0 hit points.

On a successful save, the creature becomes frightened for 1 minute. At the end of each of its turns, the target can make another Charisma saving throw. On a success, the creature is no longer frightened.

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