Ancient Coatl Dragon

Drakhan Resistance. The dragon has advantage on all saving throws against spells and other magical effects and is immune to the maze spell.

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

Spellcasting

The dragon casts one of the following spells, requiring no material components and using Intelligence as the spellcasting ability (spell save DC 22):
At will: prestidigitation
1/day each: color spray, counterspell, dispel magic, greater invisibility, hallucinatory terrain, hold person, major image, resilient sphere, silent image, slow

Multiattack.
The dragon uses its Mystifying Presence. It then makes one Bite attack and two Claw attacks. It can replace one attack with a Tail Lasso attack.

Bite. Melee Weapon Attack: +8 to hit, reach 15 ft., one target.
Hit: 18 (2d10 + 7) piercing damage.

Claw. Melee Weapon Attack: +14 to hit, reach 10 ft., one target.
Hit: 14 (2d6 + 7) slashing damage.

Tail Lasso. Melee Weapon Attack: +14 to hit, reach 20 ft., one target.
Hit: 16 (2d8 + 7) bludgeoning damage, and the target is grappled (escape DC 22). The dragon can only grapple one Large or smaller creature at a time.

Mystifying Presence.
Each creature of the dragon’s choice that is within 120 ft. of the dragon and aware of it must succeed on a DC 19 Wisdom saving throw or become charmed for 1 minute. The charmed creature regards the dragon as a trusted friend. It 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 Mystifying Presence for the next 24 hours.

Breath Weapons (Recharge 5–6)

The dragon uses one of the following:

• Dragonfire. The dragon breathes fire in a 90-foot cone. Each creature must make a DC 21 Dexterity saving throw, taking 56 (16d6) fire damage on a failed save, or half as much on a successful one.

• Blue Flame Sphere. The dragon breathes a sphere of cerulean flames around itself in a 60-foot radius. Each creature must make a DC 21 Dexterity saving throw, taking 45 (10d8) fire damage on a failed save, or half as much damage on a successful one.

• Lance of Disruption. The dragon breathes a magic beam in a 60-foot line that is 10 feet wide. Each creature must make a DC 21 Wisdom saving throw, taking 45 (7d12) force damage on a failed save, or half as much on a successful one. Every spell of 3rd level or lower ends on creatures and objects of the dragon’s choice in that area.

Elemental Redirection (3/Day).
If the dragon succeeds on a saving throw against a spell or effect that deals acid, cold, fire, lightning, or thunder damage, it can divert some of the energy. The damage the dragon takes is reduced by 34 (5d10 + 7). The dragon then immediately makes a ranged spell attack against one target it can see within 15 ft. The modifier for this attack roll is +14. On a hit, the target takes damage of the same type equal to the amount of damage the dragon reduced.

The dragon can take 3 legendary actions, choosing from the options below. Only one legendary action can be used at a time and only at the end of another creature’s turn. It regains spent legendary actions at the start of its turn.

• Tail Attack. The dragon makes a Tail Lasso attack.

• Wing Attack (Costs 2 Actions). Each creature in a 15-foot radius must succeed on a DC 22 Strength saving throw or take 12 (2d6 + 7) bludgeoning damage and be knocked prone. The dragon can then fly up to half its flying speed.

• Arcana Costs (3 Actions). The dragon either uses its Spellcasting action or it chooses one Medium or smaller object that isn’t being worn or carried and can see within 60 ft. The object magically flies up to 30 ft. directly toward the target and hits it. The target must succeed on a DC 21 Dexterity saving throw or take 31 (9d6) bludgeoning damage.