Chaos Dragon

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

Chaos Mutations. Chaos dragons may have additional mutant features. Choose or roll 1d6 on the table below.

1) Acid Boils: A creature that hits the chaos dragon with a melee attack must make a successful DC 15 Dexterity saving throw or take 7 (2d6) acid damage, or half damage on a successful save.

2) Tentacular Tongue: Instead of a bite attack, the chaos dragon has a tongue attack. Melee weapon attack: +14 to hit, reach 10 ft., one target. Hit: 19 (1d10+8) bludgeoning damage, and the target is grappled and restrained. The chaos dragon can have only one target restrained in this way. 

3) Covered in Slime: Increase the chaos dragon's AC by 2.

4) Acid Saliva: The chaos dragon's bite or tongue attack deals an extra 7 (2d6) acid damage.

5) Venomous: The chaos dragon can spit venom as a bonus action. RangedWeapon Attack: + to hit, range 30/90 ft., one target. Hit: 13 (2d12) poison damage, and the target must succeed on a DC 21 Constitution saving throw or be poisoned for one minute.

Regeneration: The chaos dragon reigns 20 hit points at the start of it's turn if it has at least 1 hit point. 

Two Heads: The chaos dragon has advantage on Wisdom (Perception) checks and on saving throws against being blinded, charmed, deafened, frightened, stunned, and knocked unconscious.

Multiattack. The chaos dragon can use its Frightful Presence. It then makes four attacks: two with it's bite (or tongue) and two with it's claws.

Bite. Melee Weapon Attack: +14 to hit, reach 10 ft., one target. Hit: 19 (2d10 + 8) piercing damage plus 2 (2d6) necrotic damage.

Claw. Melee Weapon Attack: +14 to hit, reach 5 ft., one target. Hit: 15 (2d6 + 8) slashing damage. 

Tail. Melee Weapon Attack: +14 to hit, reach 15 ft., one target. Hit: 15 (2d6 + 8) bludgeoning damage.

Frightful Presence. Each creature of the dragon's choice that is within 120 ft. of the dragon and is aware of it must succeed on a DC 19 Wisdom saving throw or be frightened of it 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.

Nectrotic Breath (recharge 5-6). The chaos dragon exhales pure necrotic energy in a 60-foot cone. Each creature in that area must make a DC 21 Dexterity saving throw. On a failure, each creature takes 63 (18d6) necrotic damage, and the it's maximum hit points are reduced by the amount of damage taken until it finishes a long rest. On a successful save, the target takes half damage and it's hit point maximum is not reduced.

Legendary Actions (3/Turn). The chaos 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 chaos dragon regains spent legendary actions at the start of it's turn.

Detect (Costs 1 Action). The chaos dragon makes a Wisdom (perception) check.

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

Wing Attack (Costs 2 Actions). The chaos dragon beats its wings. Each creature within 10 ft. of the dragon must succeed on a DC 22 Dexterity saving throw or take 15 (2d6 + 8) bludgeoning damage and be knocked prone. The chaos dragon can then fly up to half it's flying speed.