Ursula

Amphibious. Ursula can breathe air and water.

Innate Spellcasting. Ursula's innate spellcasting ability is Charisma (spell save DC 16). She can innately cast the following spells, requiring no material components:

At-will: friends, fog cloud, vicious mockery, reduce, shape water, summon beast (Flotsam and Jetsam)

1/day each: charm person, regenerate, true polymorph, enlarge

Shapechanger. Ursula can use her action to magically polymorph into a humanoid or beast that has a challenge rating no higher than her own, or back into her true form. She reverts to her true form if she dies. Any equipment she is wearing or carrying is absorbed or borne by the new form (Ursula's choice).

In a new form, Ursula retains her alignment, hit points, hit dice, ability to speak, proficiencies, legendary resistance, lair actions, and intelligence, wisdom, and charisma scores, as well as this action. Its statistics capabilities are otherwise replaced by those of the new form, except any class features or legendary actions of that form.

Horrific Appearance. Any humanoid that starts its turn within 30 feet of Ursula and can see Ursula's true form must make a DC 11 Wisdom saving throw. On a failed save, the creature is frightened for 1 minute. A creature can repeat the saving throw at the end of each of its turns, with disadvantage if the hag 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 hag's Horrific Appearance for the next 24 hours.

Unless the target is surprised or the revelation of Ursula's true form is sudden, the target can avert its eyes and avoid making the initial saving throw. Until the start of its next turn, a creature that averts its eyes has disadvantage on attack rolls against Ursula.

Multiattack. Ursula makes two tentacle attacks.

Tentacle. Melee Weapon Attack: +9 to hit, reach 10 ft., one target. Hit: 5 (2d8 + 3)  bludgeoning damage. If the target is a Medium or smaller creature it is grappled (escape DC 16). Until this grapple ends, the target is restrained, and Ursula can't use this tentacle on another target (Ursula has six tentacles). If this attack is a critical hit, the target also can't breathe or speak until the grapple ends.

Death Glare. Ursula targets one frightened creature she can see within 30 feet of her. If the target can see Ursula it must succeed on a DC 11 Wisdom saving throw against this magic or drop to 0 hit points

Lightning Storm. Ursula magically creates 3 bolts of lightning, from the trident, each of which can strike a target Ursula can see within 120 feet of her. A target must make a DC 16 saving throw, taking 22 (4d10) lightning damage on a failed save, or half as much damage on a successful one.

Ursula 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. Ursula regains spent legendary actions at the start of her turn.

Tentacle Attack. Ursula makes a tentacle attack.

Lightning Storm (Costs 2 Actions). Ursula uses Lightning Storm. However, she must be wielding the trident.

Frighten Foe (Costs 2 Actions). Ursula targets one enemy she can see within 30 feet of her. If the target can see and hear her, the target must succeed on a DC 16 Wisdom saving throw or be frightened until the end of Ursula's next turn.