Bewilder Beast

Legendary Resistance (3/Day). If the Bewilder Beast fails a saving throw, it can choose to succeed instead.

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

Siege Monster. The Bewilder Beast deals double damage to objects and structures.

Ice Breaker. The Bewilder Beast can attack ice without using an action once per turn and deals double damage to ice. This effect stacks with Siege Monster allowing for quadruple damage to ice-based structures. 

Lumbering Beast. The Bewilder Beast can only turn up to 90 degrees per turn on land and in water it turns up to 180 degrees per turn. 

Multiattack. The Bewilder Beast can use its Frightening Roar. It then makes up to four attacks with the following limitations: one with its bite, two with its claws, one with its horns, one tail sweep, and one tail smash. It can use its Swallow instead of its bite. 

Bite. Melee Weapon Attack: +19 to hit, reach 10 ft., one target. Hit: 36 (4d12 + 10) piercing damage. If the target is a creature, it is grappled (escape DC 20). Until this grapple ends, the target is restrained, and the Bewilder Beast can’t bite another target.

Claw. Melee Weapon Attack: +19 to hit, reach 15ft., one target. Hit: 26 (3d10 + 10) slashing damage.

Horns. Melee Weapon Attack: The Bewilder Beast sweeps his head down to hit anything in a 10-foot quarter-circle. The middle point of the circle is at the head. +19 to hit, reach 10ft. Hit: 24 (4d6 + 10) bludgeoning damage. If the target is a creature, it must succeed on a DC 20 Strength saving throw or be knocked prone.

Tail Sweep. Melee Weapon Attack: The Bewilder Beast attacks in a 25-foot three-quarter circle from the base of the tail and hits all creatures behind him in range. +19 to hit, one target. Hit: 24 (4d6 + 10) bludgeoning damage. If the target is a creature, it must succeed on a DC 20 Strength saving throw or be thrown 20 feet into the air. 

Tail Smash. Melee Weapon Attack: The Bewilder Beast attacks in a 25-foot semicircle from the base of the tail that can hit any one creature behind him in range. +19 to hit, one target. Hit: 36 (4d12+10) bludgeoning damage. If the target is a creature, it must succeed on a DC 20 Strength saving throw or be knocked prone.

Frightening Roar. Every creature within 100 feet of the Bewilder Beast must succeed on a DC 18 Wisdom saving throw or become frightened for 1 minute. A creature of level 12/CR 10 or lower automatically fails when the Bewilder Beast roars. A creature can repeat the saving throw at the end of each of its turns, with disadvantage if the Bewilder Beast is within line of sight, 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 Bewilder Beast’s Frightening Roar for the next 24 hours.

Swallow. The Bewilder Beast makes one bite attack against a Large or smaller creature it is grappling. If the attack hits, the target takes the bite’s damage, the target is swallowed, and the grapple ends. While swallowed, the creature is blinded and restrained, it has total cover against attacks and other effects outside the Bewilder Beast, and it takes 55 (10d10) acid damage at the start of each of the Bewilder Beast turns.

If the Bewilder Beast takes 60 damage or more on a single turn from a creature inside it, the Bewilder Beast must succeed on a DC 22 Constitution saving throw at the end of that turn or regurgitate all swallowed creatures, which fall prone in a space within 10 feet of the Bewilder Beast. If the Bewilder Beast dies, a swallowed creature is no longer restrained by it and can escape from the corpse by using 30 feet of movement, exiting prone.

Cold Breath (Recharge 5–6). The Bewilder Beast exhales an icy blast in a 90-foot cone. Each creature in that area must make a DC 22 Constitution saving throw, taking 78 (12d12) cold damage on a failed save, or half as much damage on a successful one.

Ice Beam (Recharge 6). The Bewilder Beast charges up a beam the turn it activates this attack. In the next round when it's The Bewilder Beast's turn it shoots out a large beam of ice and hail that covers a 600-foot-long cylinder with a radius of 10 feet. Each creature in that area must make a DC 25 Constitution saving throw, taking 97 (15d12) cold damage and 97 (15d12) piercing damage on a failed save, or half as much damage on a successful one. This attack also freezes most liquids it hits.

Cold Shield. (Recharge 4-6) When a creature attacks the Bewilder Beast with fire it can lower its body temperature to absorb some of the heat and only take half damage.

The Bewilder Beast 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 Bewilder Beast regains one legendary action at the start of its turn.

Attack. The Bewilder Beast makes one claw, tail, or horn attack. 

Move. The Bewilder Beast moves up to its full speed.

Cold Breath (Costs 2 Actions). The Bewilder Beast makes one Cold Breath attack. 

Ice Beam (Costs 3 Actions). The Bewilder Beast starts one Ice Beam attack. 

The Bewilder Beast can make one mythic action per day. Can only be used at the end of its turn.

Blizzard. The Bewilder Beast fires a beam of ice and snow into the air causing a raging blizzard to engulf the surrounding area for miles this lasts for 1 hour. It is unaffected by its blizzard, which causes the area to become difficult terrain from the immense amount of snow and it heavily obscures vision. Creatures also take 2d8 cold damage unless they succeed at a constitution saving throw which then they take half damage. If the creature is wearing appropriate clothes for Antarctic environments they take half damage to the blizzard. The damage occurs either at the end of the Bewilder Beast or the player's turn, choice is up to the DM.