Behemoth King

Magic Resistance. The Behemoth King has advantage on saving throws against spells and other magical effects.

Siege Monster. The Behemoth King deals double damage to objects and structures.

Dying Breath. When the Behemoth King is reduced to 0 hit points, it releases a final barrage of meteors mimicking the Meteor Swarm spell. Each creature in four 40-foot-radius spheres within range must make a DC 18 Dexterity saving throw, taking 70 (20d6) fire damage and 70 (20d6) bludgeoning damage on a failed save, or half as much damage on a successful one.

Multiattack. The Behemoth King makes four attacks: two with its claws, and one with either its bite or gore, and one with its tail. The tail can't target someone who received a bite or gore attack. 

Bite. Melee Weapon Attack: +13 to hit, reach 10 ft., one target. Hit: 26 (3d10 + 7) piercing damage.

Claw. Melee Weapon Attack: +13 to hit, reach 10 ft., one target. Hit: 22 (3d8 + 7) slashing damage.

Gore. Melee Weapon Attack: +13 to hit, reach 10 ft., one target. Hit: 29 (4d10 + 7) piercing damage. If the target is a creature, it must succeed on a DC 18 Strength saving throw or be knocked back 30 ft. 

Tail. Melee Weapon Attack: +13 to hit, reach 10 ft., one target. Hit: 29 (2d10 + 7) piercing damage. If the target is a creature, it must succeed on a DC 18 Strength saving throw or be knocked back 30 ft. 

Storms of Rage. When the Behemoth King takes damage, a storm cloud starts to form above him. Instead of rain, the cloud begins to accumulate meteors. The Behemoth King gains a bonus action on each of its turns to summon a comet from the storm cloud. The damage and radius of the comet increase as the Behemoth King’s hit points decrease:

• Above 50% HP: Comet - Ranged Spell Attack: +10 to hit, range 120 ft., one target. Hit: 22 (4d10) fire damage and 22 (4d10) bludgeoning damage.
• Below 50% HP: Greater Comet - Ranged Spell Attack: +10 to hit, range 120 ft., one target. Hit: 33 (6d10) fire damage and 33 (6d10) bludgeoning damage.
• Below 25% HP: Meteor - The Behemoth King summons a meteor. Each creature in a 20-foot-radius sphere centered on a point the Behemoth King chooses within 120 feet must make a DC 18 Dexterity saving throw, taking 49 (9d10) fire damage and 49 (9d10) bludgeoning damage on a failed save, or half as much damage on a successful one.

The Behemoth King 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 Behemoth King regains spent legendary actions at the start of its turn.

Detect. The Behemoth King makes a Wisdom (Perception) check.

Move. The Behemoth King moves up to its speed without provoking opportunity attacks.

Swipe. The Behemoth King makes a claw attack.

Summon Comet (Costs 2 Actions). The Behemoth King summons a comet as per its Storms of Rage ability.