Adult Palladium Dragon

Legendary Resistance (3/Day, or 4/Day in Lair). If the dragon fails a saving throw, it can choose to succeed instead.

Healing. Whenever the dragon targets a creature with the Poisoned with Lesser or Greater restoration, the target creature gains 3d4 temporary hit points. Additionally, the dragon can cure any form of poison with its Greater Restoration spell even if the poison would otherwise be unable to be cured. 

Suffocating Poison. If a creature is Poisoned by the dragon, they gain the following effects: Halved movement speed, halved ability to hold breath, disadvantage on Constitution saving throws.  

Multiattack. The dragon makes three Rend attacks. It can replace one attack with [A]: its Dragon’s Song ability or [B]: a use of Spellcasting to cast Dissonant Whispers (level 2 version).

Rend. Melee Attack Roll: +10, reach 10 ft. Hit: 12 (2d6 + 5) Slashing damage plus 7 (2d6) Poison damage.

Dragon’s Song. Charisma Saving Throw: DC 18, all creatures of the dragon’s choice in a 60 foot radius. Failure: The dragon’s allies who fail this saving throw gain Draconic Inspiration, allowing them to roll 1d8 whenever they fail their next skill check or saving throw, which is then added to the roll, possibly turning a failure into a success. Its enemies who fail the saving throw are affected by Draconic Demoralization, forcing them to roll 1d8 whenever they succeed their next skill check or saving throw and then subtract the number rolled on the d8 from the triggering skill check or saving throw, possibly turning a success into a failure. 

Poison Breath (Recharge 5–6). Constitution Saving Throw: DC 18, each creature in a 60-foot Cone. Failure: 56 (16d6) Poison damage and the creature is Poisoned for 1d4+2 days. Success: Half damage only.

Spellcasting. The dragon casts one of the following spells, requiring no Material components and using Charisma as the spellcasting ability (spell save DC 19, +11 To Hit):

At Will: Detect Magic, Lesser Restoration (Range 60 ft.), Heroism (No Concentration), Dissonant Whispers (level 2 version)
3/Day: Greater Restoration
1/Day: Dream

Legendary Action Uses: 3 (4 in Lair). Immediately after another creature’s turn, the dragon can expend a use to take one of the following actions. The dragon regains all expended uses at the start of each of its turns.

Mind Invasion. The dragon uses Spellcasting to cast Dissonant Whispers (level 2 version).

Purify. Wisdom Saving Throw: DC 17, one Poisoned creature the dragon can see within 90 feet. Failure: The target creature becomes Charmed by the dragon for 1 minute. It may repeat the save at the end of each of its turns, ending the effect on itself on a success. Failure or Success: The target creature is cured of its poison.

Putrefy (Costs 2 actions). Constitution Saving Throw: DC 17, all creatures within a 30 foot radius centered at a point within 90 feet of the dragon which it can see. Failure: 18 (4d8) Poison damage and the creature is Poisoned for 1d4+2 minutes. Success: Half damage only.

Pounce. The dragon moves up to half its Speed, and it makes one Rend attack.