Animikii "Storm Bird" (Ancient)

Dive Attack. If the Storm Bird is flying and dives at least 30 feet straight toward a target and then hits it with a melee weapon attack, the attack deals an extra 35 (8d8) damage to the target.

Keen Sight. The Storm Bird has advantage on Wisdom (Perception) checks that rely on sight.

Storm Cloak. While the Storm Bird is within fog or heavy rain any attacks have disadvantage to hit. 

Lightning Wreath. When the Storm Bird is struck with a melee attack, the attacker takes 16 (4d8) lightning damage and must succeed on a DC 18 Strength or Dexterity Saving Throw (creature's choice) or be knocked prone. 

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

Multiattack. The Storm Bird makes three attacks, one with gemstone claws, one with hailstone beak, and one electrocute attack. If Gemstone claws cannot be used, another hailstone beak is used instead. 

Gemstone Claws. Melee Weapon Attack: +14 to hit, reach 10 ft., one target. Hit: 13 (3d6 +6) piercing damage and 22 (6d6 + 9) lightning damage. If the target is a Medium or smaller creature, it is grappled (escape DC 20). Until this grapple ends, the target is restrained, and the Storm Bird cannot gemstone claws another creature. 

Hailstone Beak. Melee Weapon Attack: +14 to hit, reach 5 ft., one target. Hit: 13 (3d6 +6) piercing damage and 22 (5d6 +9) cold damage. 

Electrocute. Melee Weapon Attack: +14 to hit, reach 60 ft., three targets. Hit: 14 (3d6+ 9) lightning damage and make a DC 18 Strength or Dexterity saving throw (target's choice) or be paralyzed until the end of its next turn. 

Storm Bird's Call(1/Day). The Storm Bird casts Storm of Vengeance, no concentration or components required. (Spell Save DC 18)

The Storm Bird 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 Storm Bird regains spent legendary actions at the start of its turn.

Hailstone Beak Attack. The Storm Bird makes a hailstone beak attack.

Fog Cloud. (Costs 2 Actions) The Storm Bird casts Fog Cloud (9th level) in a location it can see. 

Reverberating Thunder (Costs 3 actions). The Storm Bird lets out a deep, deafening crackle as if lightning had just struck in front of you. All creatures within 120 ft must succeed on a DC 18 Constitution saving throw or take 14 (2d6 +9) thunder damage and become deafened for 1 minute.