Ancient Blue Dragon

Desert Farer. The dragon ignores difficult terrain or obscurement caused by sand or gravel, even while flying. Additionally, it ignores the effects of extreme heat.

Dune Splitter. The dragon can remain submerged in sand and gravel for up to 4 hours. It has advantage on Stealth checks made to hide in this way, and Large or smaller creatures within 20 feet of its hiding place when it emerges must succeed on a DC 24 Dexterity saving throw or be blinded until the end of its next turn.

Legendary Resistance (3/Day). When the dragon fails a saving throw, it can choose to succeed instead. When it does, it sheds some of its scales, which turn to sand. If it has no more uses of this ability, its Armor Class is reduced to 20 until it finishes a long rest.

Innate Spellcasting. The dragons spellcasting ability is Charisma (save DC 21). It can innately cast the following spells, requiring no material components. 3/day each:blur, silent image, blight, hypnotic pattern, 1/day each:control water, mirage arcane

Multiattack. The dragon attacks once with its bite and twice with its claws. In place of its bite attack it can use Arc Lightning.

Bite. Melee Weapon Attack: +17 to hit, reach 15 ft., one target. Hit: 31 (4d10 + 9) piercing damage plus 9 (2d8) lightning damage.

Claw. Melee Weapon Attack: +17 to hit, reach 10 ft., one target. Hit: 22 (3d8 + 9) slashing damage.

Tail. Melee Weapon Attack: +17 to hit, reach 20 ft., one target. Hit: 22 (3d8 + 9) bludgeoning damage and the dragon pushes the target 10 feet away.

Arc Lightning. The dragon targets a creature within 60 feet forcing it to make a DC 24 Dexterity saving throw. The creature takes 22 (4d10) lightning damage on a failure or half damage on a success. Also on a failure the lightning jumps. Choose a creature within 30 feet of the target that hasnt been hit by this ability on this turn and repeat the effect against it possibly causing the lightning to jump again.

Lightning Breath (Recharge 5-6). The dragon exhales a 120-foot-long 10-foot-wide line of lightning. Each creature in that area makes a DC 24 Dexterity saving throw taking 94 (17d10) lightning damage on a failed save or half damage on a success. A creature that fails the save can't take reactions until the end of its next turn.

Quake. While touching natural ground the dragon sends pulses of thunder rippling through it. Creatures within 30 feet make a DC 24 Strength saving throw taking 22 (4d10) bludgeoning damage and falling prone on a failure. If a Large or smaller creature that fails the save is standing on sand it also sinks partially becoming restrained as well. A creature restrained in this way can spend half its movement to escape.

Tail Attack. When a creature the dragon can see within 10 feet hits the dragon with a melee attack, the dragon makes a tail attack against it.

The dragon can take 3 legendary actions. Only one legendary action can be used at a time and only at the end of another creatures turn. It regains spent legendary actions at the start of its turn.

Roar. Each creature of the dragons choice within 120 feet that can hear it makes a DC 21 Charisma saving throw. On a failure, it is frightened for 1 minute. A creature repeats the saving throw at the end of its turns, ending the effect on itself on a success. When it succeeds on a saving throw or the effect ends for it, it is immune to Roar for 24 hours.

Wing Attack. The dragon beats its wings. Each creature within 15 feet makes a DC 24 Dexterity saving throw. On a failure, it is pushed 10 feet away and knocked prone. The dragon can then fly up to half its fly speed.

Quake (Costs 2 Actions). The dragon uses its Quake action.