Base Class: Rogue
Soul Hunters are a kind of assassin that is is most interested in the forces of life and death, which grants them several buffing and offensive powers. By killing their foes, they can use their life essence to bolster their own abilities.
Soul Stock
At 3rd level, you can use your attacks to trap the life essence of creatures and use them to empower your attacks. After defeating a creature, the next attack you make with that weapon does an additional 1d6 radiant damage.
This damage increases to 2d6 when you reach 9th level and 3d6 when you reach 13th.
Finishing Blows
At 17th level, you have become a master at manipulating the forces of life and death. When a creature attacks you, you can use your reaction to take no damage and transfer the damage to the attacker. You can use this once until you finish a long rest.
Harvester
Starting at 3rd level, every time you defeat a monster, its life aura empowers you. Every time you kill a creature, you gain an amount of temporary hit points equal to your proficiency bonus + the CR of the creature you defeated.
Life Link
Beginning at 9th level, you have the power to fuse your soul and the soul of another creature. As an action, you can borrow the abilities of a creature you have damaged or killed within the past 24 hours. For the next hour, you have proficiency in a saving throw matching the creature's highest ability score, and you know all the languages that creature knows, if any.
Soul Sight
Starting at 13th level, you gain 30 feet of darkvision, or an additional 30 feet if you already have this feature. However, your darkvision is unique from the vision of most others. While most scenery appears in a shade of gray, any living creature within 30 feet is outlined in red, and any undead within 30 feet is outlined in blue.
In addition, if you use an opportunity attack against one of these creatures, you can use your Sneak Attack. You can do this once until you take a short or long rest.