Adult Cobalt Ghast Dragon

Amphibious. The dragon can breathe air and water.

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

Commanded to breathe: Constantly exhales pacifying smoke with a DC 18 Charisma saving throw (calm emotions)

Stench. Any creature that starts its turn within 5 feet of the ghast dragon must succeed on a DC 15 Constitution saving throw or be poisoned until the start of its next turn. On a successful saving throw, the creature is immune to the ghast dragon's Stench for 24 hours.

Turning Defiance. The ghast dragon and any ghouls within 30 feet of it have advantage on saving throws against effects that turn undead.

Multiattack. The dragon can use its Frightful Presence. It then makes three attacks: one with its bite and two with its claws.

Bite. Melee Weapon Attack: +11 to hit, reach 10 ft., one target. Hit: 17 (2d10 + 6) piercing damage plus 4 (1d8) piercing damage.

Claw. Melee Weapon Attack: +11 to hit, reach 5 ft., one target. Hit: 13 (2d6 + 6) slashing damage.  If the target is a creature other than an undead, it must succeed on a DC 15 Constitution saving throw or be paralyzed for 1 minute. The target can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.

Tail. Melee Weapon Attack: +11 to hit, reach 15 ft., one target. Hit: 15 (2d8 + 6) bludgeoning damage.

Frightful Presence. Each creature of the dragon's choice that is within 120 feet of the dragon and aware of it must succeed on a DC 16 Wisdom saving throw or become frightened for 1 minute. A creature can repeat the saving throw at the end of each of its turns, 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 dragon's Frightful Presence for the next 24 hours.

Magnetic Breath (Recharge 5–6). The dragon exhales a magnetic breath in a 100-­foot line that is 5 feet wide. Each creature in that line must make a DC 18 Dexterity saving throw, taking 44 (11d4) force damage on a failed save, or half as much damage on a successful one. Targets impacted are pushed back.

Gaseous Breath. The dragon exhales gas in a 60-foot cone. Each creature in that area must succeed on a DC 18 Constitution saving throw. On a failed save, the creatures are effected by the calm emotions spell for the next one minute. Normal spell conditions apply.

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

Detect. The dragon makes a Wisdom (Perception) check.

Tail Attack. The dragon makes a tail attack.

Wing Attack (Costs 2 Actions). The dragon beats its wings. Each creature within 10 feet of the dragon must succeed on a DC 19 Dexterity saving throw or take 13 (2d6 + 6) bludgeoning damage and be knocked prone. The dragon can then fly up to half its flying speed.