Vrum-vrum

Ice Walk. The Vrum-vrum can move across and climb icy surfaces without needing to make an ability check. Additionally, difficult terrain composed of ice or snow doesn't cost it extra movement.

Two-Headed. The Vrum-Vrum has advantage on Wisdom (Perception) checks and on saving throws against being blinded, charmed, deafened, frightened, stunned, or knocked unconscious.

Keen Hearing and Smell. The Vrum-vrum has advantage on Wisdom (Perception) checks that rely on hearing or smell.

Overwhelming Battlelust. The Vrum-vrum is immune to being frightened or charmed. If an attempt to frighten or charm it is made, the Vrum-vrum rolls with advantage on its next attack.

Charge. If the Vrum-Vrum moves at least 20 feet straight toward a creature and then hits it with both its claw attacks on the same turn, the target takes an extra 19 (3d12) slashing damage and must make a DC 16 Strength saving throw or be knocked prone. 

Multiattack. The Vrum-vrum can use its Frightful Presence. It then makes four attacks: two with its bite and two with its claws.

Bite. Melee Weapon Attack: +11 to hit, reach 10 ft., one target. Hit: 17 (2d10 + 6) piercing damage plus 4 (1d8) cold damage.

Claw. Melee Weapon Attack: +11 to hit, reach 5 ft., one target. Hit: 13 (2d6 + 6) slashing damage.

Frightful Presence. Each creature of the Vrum-vrum's choice that is within 120 feet of the dragon and aware of it must succeed on a DC 14 Wisdom saving throw or become frightened for 1 minute. A creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. If a creature's saving throw is successful or the effect ends for it, the creature is immune to the Vrum-vrum's Frightful Presence for the next 24 hours.

Cold Breath (Recharge 5–6). The Vrum-vrum exhales an icy blast in a 60-foot cone. Each creature in that area must make a DC 19 Constitution saving throw, taking 54 (12d8) cold damage on a failed save, or half as much damage on a successful one.