Reaper

Most assassins are given targets, and then seek out and destroy those targets for pay. However, some assassins take this to a whole new extreme by reaping the souls of their victims, and using them to imbue their weapons with special effects. As a Reaper you gain access to abilities tied directly to an all new resource; souls. You can use souls for a multitude of effects on the battlefield, both to aid your allies and to destroy your enemies.

Soul Stealer

Starting at level 3, when you finish a long rest you can imbue one weapon of your choice with the ability to reap souls. This takes one minute of uninterrupted magical rituals tied to the weapon. Any creature that is reduced to 0 hit points by this weapon loses their soul, and it is imbued in your weapon. You can have a maximum number of souls equal to your proficiency bonus + intelligence modifier in your weapon at a single time. Listed below are a multitude of different uses for souls.

Ripper: After making a melee attack against a creature, you can expend a soul to add additional necrotic damage equal to a roll of your sneak attack dice. If the attack would've already had sneak attack, the soul is returned to you after you deal damage. 

Shadow Cloak: As an action, you can expend a soul to gain +10 to all Stealth checks for 1 minute.

Engulfing Darkness: As a reaction, when a creature within 30 feet of you is targeted by an attack, you can expend a soul to impose disadvantage on attacks against them (including triggering attack) until the end of your next turn. 

Executioner's Curse

Reapers aren't immune to the negative effects of their unique necromancy. If you take a long rest while having 0 souls you gain the Frightened condition until at least one soul is added to your pool. While Frightened in this way, you have disadvantage on attack rolls and ability checks unless intoxicated. 

Death's Warden

Starting at level 3, you gain proficiency in Charisma (Intimidation) checks and poisoner's kits.

Grim Rejuvination

Starting at 9th level, whenever you gain a soul, you can instantly expend it to gain 1d6 hit points + your proficiency bonus. 

Expanded Soul Options

Starting at 13th level, you gain access to more abilities you can use souls with:

Soul Shield: As a bonus action, you can expend two souls to gain +3 to AC for 1 minute.

Nightmarish Apparition: As an action, you can expend two souls to force a creature to make a Wisdom Saving Throw or be frightened of you for 1 minute. DC equals 8 + Proficiency Bonus + Intelligence Modifier. 

Death's Hand: As a bonus action, you can expend two souls to gain -5 to attack rolls and +10 to all damage rolls for the next minute.

Imperfect Perfectionism

Starting at level 17, you can expend all souls (to a minimum of 6) to gain expertise in all skills for 1 minute. This can only be used once per long rest.