Devoured in Flames

You choose a point within range and hurl a grey rotting ball mixed with fire. Each creature in a 20-foot radius must make a Dexterity saving throw or take 4d6 fire damage plus an extra 4d6 necrotic damage.

If this damage reduces a creature to 0 hit points, the body is scorched in the flames and the necrotic damage ravages its soul, transforming it into a cinder soul (p.245). The cinder soul disappears after 1 minute, and while it is with you, acts on your turn and is under your control. Even if its body is scorched, the target creature can be healed normally