A blackguard epitomizes evil. they are nothing short of a mortal fiend, a black knight with the foulest sort of reputation. A blackguard is an evil villain of the first order, equivalent in power to the righteous paladin, but devoted to the powers of darkness. No one class makes the best blackguard - all that is required is a willingness to serve the forces of darkness.

 

(This class was heavily inspired by Neverwinter Nights.)

Blackguard Spells

A Blackguard loses previously gained oath spells and instead gains the following Blackguard spells at the paladin levels listed.

Paladin Level	Spells
3rd	bane, inflict wounds
5th	darkness, misty step
9th	animate dead, fear
13th	blight, charm monster
17th	contagion, flame strike

Ferocious Strike

Take a Ferocious Strike at the opponent.

Once per turn, you can deal an extra 1d6 damage to one creature you hit with a melee attack roll at the cost of a bonus action

 The number of uses is equal to your proficiency bonus

The extra damage increases as you gain Blackguard levels, as shown in the Ferocious Strike table.

LEVEL	DICE
3	1D6
6	2D6
9	3D6
12	4D6
15	5D6
18	6D6

Channel Chaos

A replacement for Channel Divinity
A Blackguard paladin of 3rd level or higher gains the following two Channel Chaos options.

Sacrificial Smite - As a bonus action you hit a creature with an attack using a weapon, you can channel your Health Points to empower a smite. the target takes an extra 2d6 damage plus your health sacrificed to add to the damage. If no health is sacrificed you take 2D6 damage instead. (You Must Take Damage for the sacrifice to work) 

Dark Blessing - As an action, the paladin channels the darkest emotions and focuses them into a vicious aura gaining resistance to bludgeoning, piercing, and slashing damage for  for 3 turns

Radiant Resistance

The blackguard gains radiant resistance

Aura of Despair

Starting at 7th level, the blackguard radiates a malign aura that causes enemies within 10 feet of them to have disadvantage on all Constitution saving throws within the blackguard’s aura.

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

Malicious Retribution

As a reaction, Channel your hatred to counter attack after getting hit by an enemy attack with 2D10 Necrotic damage.

On a successful Charisma save the target takes half damage.

Anti-Paladin

As a Bonus Action, you can imbue yourself with chaotic power giving you spectral horns and turning your eyes a fiery red, granting the benefits below for 10 minutes or until you end them (no action required). Once you use this feature, you can’t use it again until you finish a Long Rest. You can also restore your use of it by expending a level 5 spell slot (no action required).

Mortal Fiend. Once per turn you add an extra D8 plus Charisma modifier to melee attacks

Chaotic Resistance. You gain Radiant immunity and resistance to Physical damage (slashing, piercing, bludgeoning)  and Necrotic Damage

Hellfire Shroud.  When an opponent is within 5 feet of you at the start of their turn they take 1 D12 fire damage.