Chuth, the unyielding

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.

Spellcasting. Chuth is a 10th-level spellcaster that uses Intelligence as its spellcasting ability (spell save DC 18; +5 to hit with spell attacks). The mage knows the following spells from the wizard’s spell list:

1st Level (4 slots): charm person, magic missile, expeditious Retreat, detect magic

2nd Level (3 slots): hold person, misty step, detect thoughts

3rd Level (3 slots): counterspell, haste, sending, fireball

4th Level (3 slots): banishment, greater invisibility, blight

5th Level (2 slots): steel wind strike, cone of cold, dawn

Multiattack. Chuth 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 7 (2d6) poison damage.

Claw. Melee Weapon Attack: +11 to hit, reach 5 ft., one target. Hit: 13 (2d6 + 6) slashing damage.

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. If the save happens in the dragon's lair, the DC changes to DC 22 Wisdom saving throw. 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.

Poison Breath (Recharge 5–6). Chuth exhales poisonous gas in a 60-foot cone. Each creature in that area must make a DC 18 Constitution saving throw, taking 56 (16d6) poison damage on a failed save, or half as much damage on a successful one.

Chuth 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. Chuth regains spent legendary actions at the start of its turn.

Detect. Chuth makes a Wisdom (Perception) check.

Tail Attack. Chuth  makes a tail attack.

Wing Attack (Costs 2 Actions). Chuth beats its wings. Each creature within 10 feet of the dragon must succeed on a DC 19 Dexterity saving throw or take 15 (3d6 + 6) bludgeoning damage and be knocked prone. The dragon can then fly up to half its flying speed.