Bellyan, the mother of dragons

Amphibious. Bellyan can breathe air and water.

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

Magic Resistance. Bellyan has advantage on saving throws against spells and other magical effects.

Reflective Carapace. Any time Bellyan is targeted by a magic missile spell, a line spell, or a spell that requires a ranged attack roll, roll a d6. On a 1 to 5, Bellyan is unaffected. On a 5 and 6, Bellyan is unaffected, and the effect is reflected back at the caster as though it originated from Bellyan, turning the caster into the target.

Siege Monster. Bellyan deals double damage to objects and structures.

Multiattack. Bellyan can use its Frightful Presence. It then makes five attacks: one with its bite, two with its claws, one with its horns, and one with its tail. It can use its Swallow instead of its bite.

Bite. Melee Weapon Attack: +22 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 Bellyan can't bite another target.

Claw. Melee Weapon Attack: +21 to hit, reach 15ft., one target. Hit: 28 (4d8 + 10) slashing damage.

Tail. Melee Weapon Attack: +21 to hit, reach 20ft., one target. Hit: 24 (4d6 + 10) bludgeoning damage. If the target is a creature, it must succeed on a DC 24 Strength saving throw or be knocked prone.

Frightful Presence. Each creature of the Bellyan's choice within 120 feet of it and aware of it must succeed on a DC 20 Wisdom saving throw or become frightened for 1 minute. A creature can repeat the saving throw at the end of each of its turns, with disadvantage if Bellyan 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 Bellyan's Frightful Presence for the next 24 hours.

Swallow. The Bellyan 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 of Bellyan, and it takes 56 (16d6) acid damage at the start of each of Bellyan's turns.

If Bellyan takes 60 damage or more on a single turn from a creature inside it, Bellyan must succeed on a DC 20 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 Bellyan. If Bellyan dies, a swallowed creature is no longer restrained by it and can escape from the corpse by using 30 feet of movement, exiting prone.

Primordial Breath (Recharge 5–6). Bellyan exhales her breath in a 140-foot line that is 18 feet wide. Each creature in that line must make a DC 27 Dexterity saving throw, taking 67 (15d8) elemental damage on a failed save, or half as much damage on a successful one.

Play a d6 to set the blow element
1- Fire
2- Lightning
3- Cold
4- Acid
5- Radiant
6- Necrotic

Change Shape. Bellyan magically polymorphous in a humanoid, usually wears red kimono and is always seen with her white fan that has a challenge rating no higher than its own, or back into its true form. It reverts to its true form if it dies. Any equipment it is wearing or carrying is absorbed or borne by the new form (Bellyan's choice).

In a new form, Bellyan retains its 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 and capabilities are otherwise replaced by those of the new form, except any class features or legendary actions of that form.

Transformed:

Multiattack. Bellyan can makes three attacks: one with its claw, two with its fan or 1 hurricane

Fan. Melee Weapon Attack: +19 to hit, reach 10ft., one target. Hit: 29 (6d8 + 10) slashing damage.

Claw. Melee Weapon Attack: +19 to hit, reach 10ft., one target. Hit: 28 (4d8 + 10) slashing damage.

Hurricane. Bellyan creates a Hurricane with its fan, any creature within 50 feet of Bellyan must be succeeded in a DC 15 skill throw saving throw or take 17 (2d6 + 10) bludgeoning damage and be knocked prone.

Bellyan 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. Bellyan regains spent legendary actions at the start of its turn.

Attack. Bellyan makes one claw attack or tail attack.

Move. Bellyan moves up to half its speed.

Detect. Bellyan makes a Wisdom (Perception) check.

Chomp (Costs 2 Actions). Bellyan makes one bite attack or uses its Swallow.

Wing Attack (Costs 2 Actions). Bellyan beats its wings. Each creature within 15 feet of Bellyan must succeed on a DC 25 Dexterity saving throw or take 17 (2d6 + 10) bludgeoning damage and be knocked prone. Bellyan can then fly up to half its flying speed.