When you or an ally within 10 feet of you reduces an enemy to 0 Hit Points, you can trade its soul to your fiendish patron for one of the following magical boons. The GM decides if a creature's soul can't be traded to a Fiend. The boon lasts for 10 minutes or until you use this feature to trade another soul.
Energy Resistance
You gain Resistance to one of the following damage types: Acid, Cold, Lightning, Necrotic, Poison, Psychic, Radiant, or Thunder.
Fortitude
You gain Temporary Hit Points equal to your Warden level.
Truesight
You have Truesight with a range of 10 feet.
Skill
You gain proficiency and Expertise in one skill of your choice.
Speed
Your Speed increases by 15 feet.