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.

Multiattack. The dragon makes three attacks: one with its bite and two with its claws.

Bite. Melee Weapon Attack: +12 to hit, reach 10 ft., one target. Hit: 23 (3d10 + 6) piercing damage.

Claw. Melee Weapon Attack: +12 to hit, reach 5 ft., one target. Hit: 17 (3d6 + 6) slashing damage.

Aura of Madness. 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 repeats the saving throw at the end of each of its turns, ending the effect on itself on a success. If a creature fails the saving throw by 5 or more it is driven insane. An insane creature is frightened permanently, and behaves as if affected by confusion while it is frightened in this way. If a creature’s saving throw is successful or the effect ends for it, the creature is immune to the dragon’s Aura of Madness for the next 24 hours.

Breath Weapons (Recharge 5–6). The dragon uses one of the following breath weapons.

Balefire Breath. The corrupted dragon vomits forth liquid fire in a 50-foot line 15 feet wide. Each creature in that area must make a DC 19 Dexterity saving throw, taking 63 (14d8) fire damage on a failed save, or half as much damage on a successful one. The area hit by the cone becomes difficult terrain and deals 2d8 fire damage each time a creature enters the area, or starts their turn in it. 

Corrupting Breath. The corrupted dragon exhales a miasma in a 30-foot cone. Each creature in that area must succeed on a DC 19 Constitution saving throw or roll a 1d6, gain one of the following mutations:

1-2: Gain an extra appendage capable of making an attack of 2d8 + strength slashing damage, or grappling the creature using its own Athletics score.

2-3: A third eye opens up in the targets forehead, giving it disturbing visions of worlds beyond comprehension. Creatures must make DC 15 concentration checks before casting a spell, the spell being wasted on a failure. 

5-6: A creature grows an additional leg that does not cooperate, halving movement speed and giving disadvantage on all dexterity checks and dexterity saves. 

Creatures can use an action to forcibly remove the extra limb with an attack. The attack automatically crits, and upon dealing 20 damage total to the limb/themselves, it is removed. 

A creature who is at 0 hit points automatically fails the save and rises as a Bagiennik under the Corrupted Gold Dragon's control. 

Bite. The dragon makes a bite attack.
Tentacle Burst (Costs 2 Actions). Tentacles reach through hidden slits in the Dragon's body and whirl around it chaotically. Each creature within 15 feet of the dragon must succeed on a DC 18 Dexterity saving throw or take 12 (2d6 + 5)
bludgeoning damage and be knocked prone. The dragon can
then teleport to an unoccupied space within 40 feet.