Black Flame Zealot

A Black Flame Zealot has gained favor from a specific deity that allows them the use a Black Flame to slay their enemies.

The Black Flame

Starting at 3rd level, you can use the bonus action granted by your Cunning Action to coat a weapon you are holding in a blackened flame. This causes the weapon coated in this flame to deal an extra 2d6 damage. This damage is both Fire and Necrotic. (If a creature has resistance or vulnerability to either, treat it as a single type.) You can use this feature a number of times equal to your proficiency bonus between long rests.

The flame lasts for a number of rounds equal to your Wisdom modifier. (Minimum 1)

Zealotry

When you choose this archetype at 3rd level, you gain proficiency in the Religion skill.

If you already have proficiency in Religion, you instead double your proficiency bonus.

Shadowstep

Starting at 9th level, You can cast Misty Step once without expending a spell slot or material components. Except you are limited to your destination being in only dim or no light. You can't do so again until you finish a short rest.

Divine Fanatacism

At 13th level,  your Black Flame now deals either Fire or Necrotic damage (your choice when you create the flame.)

In addition, you can change the the damage being dealt with your sneak attack dice to be either all Fire or Necrotic.

Sacred Conflagrancy

When you reach 17th level, your Black Flame reaches it's maximum potential. Any creature killed by fire or necrotic damage you deal is immediately and utterly consumed by profane flames. A creature slain this way may only be restored to life if someone were to use true resurrection, or a carefully worded wish spell followed by resurrection.

In addition, whenever you deal necrotic damage with your flame, the target loses fire resistance until the start of its next turn, and if you deal fire damage, the target loses necrotic resistance instead.