Avenger

The Avenger
The Avenger is a paladin that delved into dark power to better fight and understand their enemy. They're a little broody or grumpy most of the time because they are all conflicted about their faith. Not exactly the type of guy you'd want a drink with.

Devil Striker
The Avenger is the complete opposite of a normal paladin! Instead of protecting, they focus on mauling their enemies. Instead of holy power, they use the power of darkness. It's a little confusing. At 8th level, the Paladin receives several fundamental changes to their class features. Their Divine Smite now deals necrotic damage instead of radiant damage. Instead of Aura of Courage, the avenger gains an Aura of Darkness, which inflicts disadvantage on saves against fear for enemies within 10 feet (30 feet at level 18). Instead of Cleansing Touch, the Avenger gains the ability to cast Bane a number of times between long rests equal to their Charisma modifier without using any spell slots. Finally, their Lay on Hands ability is replaced with a Devil Gauge. The Devil Gauge retains a maximum amount of their Paladin level x5, but it starts empty at the end of each long rest. The Paladin receives 5 points to this Devil Gauge each time they make a successful attack or deal damage with a spell. They can spend 10 points to either add an amount of necrotic damage to an attack equal to their weapon die, or add an effective level to a damaging spell.

Echoes of Nothing
An avenger could write extensively on the darkness in their heart. In fact, a few have. In the form of poetry. It's kind of sad. At 13th level, the avenger's darkness and emptiness manifests outward whenever they roll a critical hit, or whenever an enemy rolls a 1 on a saving throw against their spells. The avenger's move speed increases by 20', they receive +2 to attack rolls, and they deal 1d10 bonus necrotic damage on all of their attacks and spells for 1 minute while the manifestation is active.

In addition, they add the following spells to their spell list.
 * Eldritch Blast
 * Hellish Rebuke
 * Witch Bolt
 * Darkness
 * Fear
 * Vampiric Touch
 * Blight

Demonize
The deeper the avenger dips into the dark arts, the harder it is not to whine incessantly about it. But still, they get some pretty cool perks, like turning into a rampaging demon. At 18th level, whenever the Paladin's Devil Gauge is full, they can expend all of it to take the form of a powerful demon. Their size increases to large, their reach increases by 5, and they gain THP equal to their paladin level. All of their attacks and spells deal necrotic damage, and they gain the automatic effects of spending 10 of their Devil Gauge to enhance their attacks and spells, and can still use their Devil Gauge in the same manner to gain an even greater bonus. This form lasts for 1 minute, and cannot be used again until the avenger takes a short rest.