Compulsion immunity. The chaos dragon is immune to all effects that would effect their way of current thinking or general way of thinking. 

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

Innate Spellcasting. The adult chaos dragon's innate spellcasting ability is Charisma (DC 18, +10 to hit with spell attacks). The adult chaos dragon can innately cast the following spells, requiring no material components:

3/day each: fire shield (deals necrotic damage), protection from good and evil (effects only lawful beings instead), spiritual weapon (deals necrotic damage and is always a hammer), 

1/day each: chaos bolt, dispel good and evil (only effects lawful beings), mislead, divine word (only effects lawful creatures)

Multi attack. The adult chaos 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., 1 target. Hit: 17 (2d10 + 6) piercing damage plus 5 (2d4) of one of the breath weapon's damage types chosen at random. 

Claw. Melee Weapon Attack: +11 to hit, reach 5 ft., 1 target. Hit: 13 (2d6 + 6) slashing damage. 

Tail. Melee Weapon Attack: +11 to hit, reach 10 ft., 1 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 18 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.

Chaotic breath (Recharges 5/6). The chaos dragon exhales a blast of chaotic energy, each creature within a 60ft cone must make a DC 19 Dexterity saving throw or take 52 (21d4) of one of the following damage types picked at random: acid, cold, lightning, fire or thunder. On a successful saving throw a creature takes half damage. 

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 (Costs 1 Action). The dragon makes a Wisdom (Perception) check.

Tail Attack (Costs 1 Action). The dragon makes a tail attack.

Maddening shift (Costs 2 Actions). The chaos dragon teleports up to 60ft into an unoccupied space that they can see and when they teleport each creature that can see them within 30ft of there location before teleporting must make a DC 19 Wisdom saving throw or be stunned until the end of their next turn.