Zack Hartford, the Ashen Vow Manifester

Ashen Vow. Zack wields a corrupted version of Ashen Vow:

• +2 bonus to attack and damage rolls
• Critical hit on 19–20
• Deals +1d6 psychic damage on every hit
• Uses Sinner’s Insight, Crimson Certainty, and Ashburst Detonation

Zack cannot use Fell Bullet on player characters. He may only use it on his own allies.

Sinner’s Insight. Zack gains 1 Sinner’s Insight stack (maximum 7) whenever a creature allied to him with CR 2 or higher dies. The stacks reset when the combat ends.

Fell Bullet. When he hit a ally creature with an attack made using Ashen Vow, you may choose to invoke Fell Bullet. If you do, the attack deal force damage equal to the target’s Hit Dice and it's modified instead of its normal damage. This damage can’t be reduced in any way and Ignores all damage immunities.

Crimson Certainty. Zack’s attacks already crit on 19–20.
Whenever Zack scores a critical hit, he deals an extra 2d6 + (Sinner’s Insight)d6 psychic damage
When Zack kills an allied creature, he enters Crimson Mode until the end of his next turn:

• His critical range becomes 18–20
• He can use Ashburst Detonation

Multiattack. Zack makes two attacks with Ashen Vow.

Ashen Vow. Ranged Weapon Attack: +10 to hit, range 150/600 ft., one target Hit: 1d12 + 6 piercing + 1d6 psychic.

Order to Die (Recharge 5–6). Zack chooses one allied creature within 60 feet. That creature must use its reaction to make one attack against a target Zack chooses. If the ally dies as a result of this action, Zack gains 2 Sinner’s Insight stacks.

Ashburst Detonation. usable only during Crimson Mode
When an allied creature Zack just killed drops to 0 HP, its body erupts in cursed ash. All creatures within 20 feet must make a Dexterity saving throw DC = 14 + Sinner’s Insight.
On a failure, a creature takes: 2d6 + (Sinner’s Insight)d6 psychic damage +2d6 fire damage. On a success, the creature takes half damage.