Bewilderbeast

Ice Walk. The dragon 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.

Legendary Resistance (4/Day). If the dragon fails a saving throw, it can choose to succeed instead.

Amphibious. The dragon can breathe both air and water.

Multiattack. The dragon can use its Frightful Presence. It then makes four attacks: one with its bite, one with its claws, one with its tusks and one with its tail.

Bite. Melee Weapon Attack: +18 to hit, reach 10 ft., one target. Hit: 32 (4d10 + 10) piercing damage plus 13 (2d12) cold damage.

Tusk. Melee Weapon Attack: +18 to hit, reach 15 ft., one target. Hit: 42 (5d12 + 10) piercing damage.

Claw. Melee Weapon Attack: +18 to hit, reach 10 ft., one target. Hit: 28 (4d8 + 10) Slashing damage.

Tail. Melee Weapon Attack: +18 to hit, reach 35 ft., one target. Hit: 36 (4d12 + 10) bludgeoning damage and the target must make a DC 26 strength save or be knocked prone.

Frightful Presence. Each creature of the dragon's choice that is within 120 feet of the dragon and aware of it must succeed on a DC 23 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 dragon's Frightful Presence for the next 24 hours.

Cold Breath (Recharge 5–6). The dragon exhales an icy blast in a 120-foot cone. Each creature in that area must make a DC 24 Constitution saving throw, taking 90 (20d8) cold damage on a failed save, or half as much damage on a successful one.

The dragon can take 3 legendary actions, choosing from the options below. Only one legendary action option can be used at a time and only at the end of another creature's turn. The dragon regains spent legendary actions at the start of its turn.

Shattering Roar. The Dragon unleashes a powerful roar. Each creature in a 120-foot-radius sphere centered on the dragon must succeed on a DC 23 Constitution saving throw or take 19 (3d12) thunder damage and be incapacitated until the start of its next turn.

Tail Attack. The dragon makes a tail attack.

Wing Attack (Costs 2 Actions). The dragon beats its wings. Each creature within 25 feet of the dragon must succeed on a DC 26 Dexterity saving throw or take 17 (2d6 + 10) bludgeoning damage and be knocked prone. The dragon can then move up to its speed.