Wield Soul

You draw forth the ebbing life force of a creature and use its arcane power. Upon casting this spell, you must touch a creature that dropped to 0 hit points since your last turn. If it fails a Wisdom saving throw, you gain knowledge of spells, innate spells, and similar abilities it could have used today were it still alive. Expended spells and abilities aren't revealed. Choose one of these spells or abilities with a casting time no longer than 1 action. Until you complete a long rest, you can use this spell or ability once, as a bonus action, using the creature's spell save DC or spellcasting ability bonus.