Death Knight

After committing a heinous act that even the evilest of cultists could never dream, your soul is ripped from your body, your body engulfed in green hellfire, and your blade fuses with your soul. As your skin and muscle tears away, you become one with your armor, and one with your blade. You have become one of the most dangerous and evil beings in the multiverse... Are you sure this is what you wanted?

Examples of beginning your oath: Killing a loved one in a manner you know they fear most, lure a group of cast out halflings to a circus and burn it to the ground with them trapped inside, bind an angel to this world and tear off their wings, etc

Tenets of a Death Knight

Fight Honorably: Never fight from the shadows. Give every opponent a fighting chance.

Fill them with Fear: You are above the common rabble. Your gaze should make them quiver.

Destroy the Hope: Death comes for everyone except you. You are an incarnation of death and everyone must know. Kill any who oppose you.

Never Lose your Blade: This weapon is your life. It binds you to this world. 

 

Undead Bond

As you complete your tenets and your deed, your body burns away in green hellfire, leaving nothing but charred bones behind. Your soul is ripped from your body, and fused into your weapon. This weapon becomes your Soul Weapon. Your Soul Weapon is your arcane focus and your bond. It grants you power and acts as a constant reminder of the heinous act you committed. If your Soul Weapon were to be stolen from you, the thief would be forced to make a Wisdom Saving through where the DC is 8 + your Spellattack Bonus every time they attempt to swing the blade. On a failure, the thief is consumed with despair, struck dumb, and motionless for the next 30 minutes. On a success, they would feel no effect.

However, while the blade is not in your possession, you become filled with despair and anger. Each day preceding the theft of your weapon, you must make a Constitution Saving Throw. The DC is 10 + the number of days the weapon is out of your possession. On a failure, your maximum Health is halved. If you have a Maximum HP of 1 and fail another Constitution Saving Throw in this manner, you die and your body and your weapon turn to ash with no Death Saving Throws. All HP lost in this way is restored if you retrieve your weapon.

Upon taking this oath, you lose the ability to cast healing magic. Any magic that would normally restore hit points to a creature automatically fails.

Undead Nature: You no longer require air, food, drink, or sleep.

Channel Divinity

When you take this oath at 3rd level, you gain the following two Channel Divinity options.

Death Weapon. As an action, you can imbue your Soul Weapon with negative energy, using your Channel Divinity. For 1 minute, you add your Charisma modifier to attack rolls made with that weapon (with a minimum bonus of +1). The weapon also emits dim purple light in a 20-foot radius. If the weapon is not already magical, it becomes magical for the duration. In addition, you may choose whether the attack deals its normal damage or necrotic damage.

You can end this effect on your turn as part of any other action. If you are no longer holding or carrying this weapon, or if you fall unconscious, this effect ends.

Turn the Holy. As an action, you present your Soul Weapon and speak a prayer censuring celestials and fey, using your Channel Divinity. Each celestial or fey that can see or hear you within 30 feet of you must make a Wisdom saving throw. If the creature fails its saving throw, it is turned for 1 minute or until it takes damage.

A turned creature must spend its turns trying to move as far away from you as it can, and it can’t willingly move to a space within 30 feet of you. It also can’t take reactions. For its action, it can use only the Dash action or try to escape from an effect that prevents it from moving. If there’s nowhere to move, the creature can use the Dodge action.

Oath Spells

You gain oath spells at the paladin levels listed. Whenever you cast a fire-based spell, the fire appears as the green hellfire that had engulfed you. Any healing spells granted to you by the Paladin Spell List automatically fail if you attempt to cast them.

Death Knight Spells

Ethereal Weapon

Starting at 7th level, once per long rest, you may choose a creature within 30 feet of you that you can see. For the next minute, you register their AC as their natural armor (example: most humanoids have a natural AC of 10+ Dex Mod, while an adult red dragon has a natural AC of 19). Your Soul Weapon phases into the Ethereal Plane whenever you go to strike this individual, dealing damage directly to them, rather than their armor. This effect ends if you target someone else with an attack. 

At 18th level, if you reduce a target to 0 HP with your Ethereal Weapon ability, you may target another creature with this ability.

Shield of Shadows

Beginning at 15th level, you are always under the effects of an Armor of Agathys spell. At the beginning of your turn in combat, you regain the temporary hit points. In addition, the damage dealt by this spell is necrotic rather than cold.

Aura of Death

At 20th level, you can use your Channel Divinity to cast Circle of Death centered on you.

You may choose any number of creatures to not be affected by the spell.

If a creature dies from the spell, you may use your reaction to cast the spell again.