Death Knight

There are cases where a paladin may fall, may succumb to darkness one way or another. They either get their souls stolen by nefarious beings, or they simply get tainted by shadow. These falls are not always on purpose, and when they are, are rarely for any nefarious intent. More often than not, paladins find their holiness stolen, either being corrupted by darkness but retaining their will, or they lose their souls entirely and death fuels them from then on. They are not undead, per se, but death does become their closest ally. They wield its powers and those of shadow as easily as they once wielded the Light.

Some death knights continue to serve the Light, in roundabout ways, by doing things on its behalf that paladins normally could not do. Others do their own will, either remaining good to some extent or losing hope and becoming true shadows. Either way, they're no longer pure in the Light, and lose the ability to wield their once holy powers. In the Light's stead, they gain access to dark or elemental powers, wielding the might of the arcane and the foul magics of undeath. 

Aura of Frost

Starting at 10th level, you exude a cold atmosphere that slows down unfriendly creatures within 15 feet of you. Enemies making melee attacks on you must make Constitution saving throws with a DC of 15, or else they have trouble breathing, allowing for advantages on attack against them. You must be conscious to give this effect, and anyone who's your friendly is unaffected by the cold.

At 20th level, the range extends to 30 feet, and you can make a shell of icy armor for one round as a bonus action.

Dark Horse

You tap into the shadows within you, becoming a juggernaut of sheer shadow. The shadows strengthen your body, your muscles, and your mind. As a bonus action, you can activate Dark Horse on your turn.

While Dark Horse is activated, you get the following advantages if you wear heavy armor.

• You get advantages on Strength checks and saving throws, and Constitution and Intelligence saving throws.
• When you make a magical attack roll using Charisma, you gain an additional damage die for every additional level.
• You have resistance to bludgeoning and slashing damage, and to all spell-types.
• You become vulnerable to Radiant Damage.

It lasts until deactivated, or until the user is sleeped or knocked unconscious, but requires a long rest to be replenished. It can be dispelled by a spell if the caster makes the DC of 18.

Channel Death

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

Bone Weapon. As an action, you can imbue one weapon that you are holding with deathly energy, using your Channel Death For 1 minute, you add your Charisma modifier to attack rolls made with that weapon (with a minimum bonus of +2). If the weapon is not already magical, it becomes magical for the duration.

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 Unholy. As an action, you present your holy symbol and speak a prayer censuring fiends and undead, using your Channel Death. Each fiend or undead 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.

Death Magicks

You gain death magicks at the death knight levels listed.

Death Magicks

DEATH KNIGHT LEVEL	SPELLS
3rd	absorb elements, bane, spirit guardians, dominate beast
5th	animate dead, dominate beast, blight, dominate person
9th	create undead, dispel magic, dominate monster
13th	water walk, call lightning
17th	speak with dead, flame strike

Aura of Shadow

Starting at 7th level, you and friendly creatures within 15 feet of you get advantage on Dexterity (Stealth) checks while you are conscious.

At 18th level, the range of this aura increases to 30 feet.

Purity of Death

Beginning at 15th level, you are always under the effects of a Protection From Energy spell.

Revenant King

You embody Death itself, you're more than just its harbinger and its herald now...you. Are. Death.

At 20th level, you take on a powered up form, gaining 10+ to your total AC, and increasing your movement speed by 10 feet. You're nigh on demonic appearance as you embody Death strikes fear into the hearts of enemy creatures within 30 feet of you, unless they make a DC 20 Wisdom Saving Throw. It lasts for 2 minutes, and it fades with a cold blast that causes 3d10 Cold Damage to enemy creatures within 15 feet.

In addition, for the duration, you have advantage on saving throws against spells cast against you. You do become vulnerable to Radiant Damage, however.

Once you use this feature, you can't use it again until you replenish it.