Thank you TyfloRen for showcasing the Mod!

Tenets

Oath of Treachery paladins abide by the following tenets:

Necrotic Sovereignty.

I swear to command necrotic energies, using dark rituals to curse and corrupt, leaving desolation in my wake.

Soul Exploitation.

I vow to harness the souls of others as a wellspring of power, viewing them solely as tools to amplify my abilities.

Self-Centered Devotion.

 I forsake service to higher causes, dedicating loyalty to personal power, wealth, and dark desires.

Worship of Malevolence.

I worship unholy forces, seeking the favor of the darkness for blessings to enhance my power.

Spell List

Level 3

Charm Person, Ray Of Sickness

Level 5

Mirror Image, Invisibility

Level 9

Blink, Hypnotic Pattern

Level 13

Phantasmal Killer, Greater Invisibility

Level 17

Dominate Person, Planar Binding

Oath Passive Ability

Level 1

Soul Drinker

Your Oath twists the confines of your very soul. You feel a deep hunger for the souls of everyone around you. Once per turn, you regain 1d6 + your Charisma modifier when you kill a target.

Oath Spells

Level 1

Soul Reflection

Your connection to the unholy grants you abilities from tormented souls. You gain access to an expanded spell list that consumes your Channel Oath.

Level 3

Friends in Low Places

You grab an unwilling soul to serve as your undead servant. You can only use this ability outside of combat.

Necrosurge

Your soul rips open to be fueled with the souls of the fallen. You are reduced to half your HP and gain bonus 1d4 necrotic and 1d4 poison + your Charisma modifier on all your weapon attacks. Enemies that hit you have a chance of becoming Poisoned. The duration of the skill increases with your Paladin level.

Level 7

Aura of the Despair

You gather souls around you to fight against your enemies. While this aura is active, you gain Advantage when there is 1 or more allies around an enemy. While within 3m of the aura, enemies will take 1d4 Necrotic damage on a failed Constitution Saving Throw. On a successful save, they will still take half damage.

Level 15

Soul Ripper

You take the very essence of another soul to fuel your power. On a successful attack roll, you deal 5d6 Necrotic Damage and heal on the amount damaged. You deal half the amount of damage on a failed roll. After gaining their essence, you gain access to an expanded spell list for 3 turns. You can't use this feature again until a short rest.

Level 20

Icon of Betrayal

You become an avatar of conceit, treachery, and hatred. For 1 minute, you become Invisible, gain Advantage on Stealth checks, Immunity to Necrotic, Poison, and Acid damage, you can see through magical darkness, and gain bonus damage based on your Charisma modifier. You can't use this feature again until a long rest.

Oathbreaking

There is no oathbreaking. You are tagged as an Oathbreaker, You cannot respec your character because of how Larian tagged Oathbreaker mechanics. If you want to respec your character try the Respec mod. Otherwise, be very careful about choosing this class.

FAQ

I can't change my class! How can I change it?

There is no oathbreaking. You are tagged as an Oathbreaker, You cannot respec your character because of how Larian tagged Oathbreaker mechanics. If you want to respec your character try the Respec mod. Otherwise, be very careful about choosing this class.

Can your mods work with other Paladin mods?

All of my mods work with other mods that are updated with Community Library. Make sure that Community Library is first on your load order and the Compatibility Framework Mod comes after my paladin mods. If you want more flexibility - download Plus Subclasses - Previewer by Raizan. They're good people and have awesome mods you should check out.

Does it work with Patch 5?

Yes! Make sure you have everything else updated.

I have a feature request! 

Sure, please know that I may not always add them in if involves wildly changing the subclass, or I'm busy working on other projects.

I love your mods, I want to share an idea for a subclass/class!

Thank you for your support! If you have an idea for me, please DM me and we can work out a possible commission for your subclass idea. Unfortunately, I have other freelance work that keeps me busy, so if you want your mod done quickly, Nitreaux does subclass mod commissions. If you'd still like me to take you on as a client, I'd be happy to hear your subclass ideas.

Will you make "X" subclass?

Possibly, right now my main jam is Paladins, so most likely I'll make my version of the class.

Your subclass is overpowered/unbalanced/etc.

Thank you for your feedback, I'll try to make changes where I can. But to be clear, I'm not Larian or WotC, I make things I like and I think that would be fun. If you're not a fan, I can respect that but I'll stick by my work. 

Why is this subclass not just written the way the UA was?

Few reasons, the limitations of what BG3 can do compared to 5e, and I like to take creative liberties with Paladins. I love making them more flavorful and unique to what is already out there.

Final Notes

This mod is fully loaded with its own class icons and CF compatibility!

Installation Instructions (Using Vortex/BG3 Mod Manager)

• Download and Extract OathofTreachery.zip
• Have Community Library and Compatibility Framework installed. Make sure Community Library is loaded in first in your mod load order. Compatibility Framework should loaded after all modded subclasses supporting CF.
• Drop files in Vortex or into the inactive mod section of BG3MM. Move into active mod section (BG3MM).
• Save Load Order to File and launch the game. The subclass should appear in character selection.
  

Please submit any images you have, I would love to feature them on the mod page!

Special Thanks

Very special thanks to Siael for answering all my questions and being a modding wizard.
ImmortalRD for creating an amazing VFX guide that helped me out - BG3 VFX wiki
KiderionLykon for the Class Icon Generator
WotC for their UA Oath of Treachery subclass!

havsglimt and BigGreenMako for inspiring me with their amazing mods.
Everyone on the discord chat community for being so helpful and knowledgeable. 
Norbyte for their tireless work to make modding a reality for this amazing game.
Last but not least Larian Studios for making me fall in love with this game!