Adult Blue Dragon

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

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.

The dragons spellcasting ability is Charisma (save DC 18). It can innately cast the following spells, requiring no material components.
- 3/Day Each: Blur, Silent Image, Blight, Hypnotic Pattern

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 17 until it finishes a long rest.

The dragon targets a creature within 60 feet forcing it to make a DC 20 Dexterity saving throw. The creature takes 16 (3d10) 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.

Melee Weapon Attack: +13 to hit, reach 10 ft., one target. Hit: 23 (3d10 + 7) piercing damage plus 4 (1d8) lightning damage.

Melee Weapon Attack: +13 to hit, reach 5 ft., one target. Hit: 20 (3d8 + 7) slashing damage.

The dragon exhales a 90-foot-long 5-foot wide-line of lightning. Each creature in that area makes a DC 20 Dexterity saving throw taking 77 (14d10) 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.

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

Melee Weapon Attack: +13 to hit, reach 15 ft., one target. Hit: 16 (2d8 + 7) bludgeoning damage and the dragon pushes the target 10 feet away.

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 uses its Quake action.

Each creature of the dragons choice within 120 feet that can hear it makes a DC 18 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.

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.

The dragon beats its wings. Each creature within 15 feet makes a DC 20 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.