Bane of the Undying

A 20-foot-radius sphere of fog appears within range of you until a wind of at least 10 miles per hour blows it away, or until the spell ends. The fog is centered on a point you choose, spreading around corners and heavily obscuring the area it fills and preventing creatures inside from regaining hit points in any way. If a creature leaves the area they still cannot regain any hit points until the end of their next turn. Temporary hit point are not affected by this spell.