Ancient Astral Dragon Turtle

Amphibious. The dragon turtle can breathe air and water.

Astral Bloodline. While in the astral plane the dragon turtle has a speed of 20 + it's movement.

Astral Entity. The dragon turtle can't leave the Astral Plane, nor can it be banished or otherwise transported out of the Astral Plane.

Energetic Shell. Any time the dragon turtle is targeted by a spell that requires a ranged attack roll or a charisma saving throw, and the spell fails. The next attack by the dragon turtle will deal an extra 1d6 force damage for each spell level above 1st.

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

Magic Weapons. A dragon turtle's weapon attacks are magical.

Reflective Shell. Any time the dragon turtle 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 3, the dragon turtle is affected. On a 4 to 6, the dragon turtle is unaffected, and the effect is reflected back at the caster as though it originated from the dragon turtle, turning the caster into the target.

Siege Monster. The dragon turtle deals double damage to objects and structures.

Voidborn. The dragon turtle has its own gravity, and does not require air to live.

Multiattack. The dragon turtle makes three attacks: one with its bite and two with its claws. It can make one tail attack in place of its two claw attacks, or use it's shell defense action in place of it's claw attacks.

Bite. Melee Weapon Attack: +16 to hit, reach 15 ft., one target. Hit: 23 (2d12 + 9) piercing damage. If the target is a creature, it is grappled (escape DC 20). Until this grapple ends, the target is restrained, and the dragon turtle can't bite another target.

Claw. Melee Weapon Attack: +16 to hit, reach 10 ft., one target. Hit: 18 (2d8 + 9) slashing damage.

Tail. Melee Weapon Attack: +16 to hit, reach 15 ft., one target. Hit: 28 (3d12 + 9) bludgeoning damage. If the target is a creature, it must succeed on a DC 22 Strength saving throw or be pushed up to 10 feet away from the dragon turtle and knocked prone.

Sorcerous Storm. The dragon turtle magically creates 5 bolts of magical energy from it's shell, each of which can strike a target the dragon turtle can see within 120 feet of it. A target must make a DC 19 Dexterity saving throw, taking 22 (4d10) force damage on a failed save, or half as much damage on a successful one.

Fling. One Large or smaller object held or creature grappled by the dragon turtle is thrown up to 60 feet in a random direction and knocked prone. If a thrown target strikes a solid surface, the target takes 4 (1d8) bludgeoning damage for every 10 feet it was thrown. If the target is thrown at another creature, that creature must succeed on a DC 16 Dexterity saving throw or take half the same damage and be knocked prone.

Shell Defense. The dragon turtle can withdraw into it's shell as an action. Until it emerges, the dragon turtle gains a +8 bonus to AC, and it has advantage on Strength and Constitution saving throws. While in the shell, the dragon turtle's speed is halved, it has disadvantage on Dexterity saving throws, it can’t take reactions, any attacks are made at disadvantage, and the dragon turtle can use a bonus action to emerge from the shell.

Swallow. The dragon turtle 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 dragon turtle, and it takes 39 (6d12) acid damage at the start of each of the dragon turtle's turns.

If the dragon turtle takes 50 damage or more on a single turn from a creature inside it, the dragon turtle must succeed on a DC 25 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 dragon turtle. If the dragon turtle dies, a swallowed creature is no longer restrained by it and can escape from the corpse by using 30 feet of movement, exiting prone.

Steam Breath (Recharge 5–6). The dragon turtle exhales scalding steam in a 60-foot cone. Each creature in that area must make a DC 19 Constitution saving throw, taking 52 (15d6) fire damage and 52 (15d6) force damage on a failed save, or half as much damage on a successful one. Being underwater doesn't grant resistance against this damage.

The dragon turtle 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 dragon turtle regains spent legendary actions at the start of its turn.

Attack. The dragon turtle makes one claw attack or tail attack.

Chomp (Costs 2 Actions). The dragon turtle makes one bite attack or uses its Swallow.

Sorcerous Storm (Costs 2 Actions). The dragon turtle uses it's Sorcerous Storm.

Powerful Luminosity (Costs 3 Actions). The dragon turtle uses it's shell defense and sheds bright light from it's shell, illuminating in a 30-foot radius. The light is so strong that any creature standing from 30 feet away and looking at the dragon turtle must succeed on a DC 19 Constitution saving throw or be blinded until the start of the creature's next turn. If the creature decides to not look at the dragon turtle it can automatically succeed the saving throw at the start of its turn, but it will have disadvantage on attack rolls against it until the start of its next turn.