Swarm of Wolf Spirits

Incorporeal Movement. The swarm of wolf spirits can move through other creatures and objects as if they were difficult terrain. It takes 5 (1d10) force damage if it ends its turn inside an object.

Swarm. The swarm can occupy another creature's space and vice versa. The swarm can't regain hp or gain temporary hp.

Undead Nature. The swarm of wolf spirits doesn't require air, food, drink, or sleep.

Multiattack. The swarm of wolf spirits makes two Spectral Bites attacks.

Spectral Bites. Melee Weapon Attack: +7 to hit, reach 0 ft., one creature in the swarm's space. Hit: 14 (4d6) cold damage plus 9 (2d8) necrotic damage, or 7 (2d6) cold damage plus 4 (1d8) necrotic damage if the swarm has half of its hp or fewer.

Chilling Howl (Recharge 5-6). The swarm of wolf spirits howls, causing cold fear to course through those that hear it. Each creature within 15 feet that can hear the howl must make a DC 15 Constitution saving throw. On a failure, a creature takes 35 (10d6) cold damage and is frightened for 1 minute. On a success, a creature takes half the damage and isn't frightened. A creature that fails the saving throw by 5 or more also suffers one level of exhaustion. A frightened creature can make a DC 15 Wisdom saving throw at the end of each of its turns, ending the effect on itself on a success.