Adult Green Dragon

Huge Dragon, lawful evil

AC: 19 (natural armor)
HP: 207 (18d12 + 90)
Speed: 40 ft., fly 80 ft., swim 40 ft.

STR	DEX	CON	INT	WIS	CHA
23 (+6)	12 (+1)	21 (+5)	18 (+4)	15 (+2)	18 (+4)

Saves: Str +6, Dex +6, Con +5, Int +4, Wis +7, Cha +4
Skills: Deception +9, Perception +12, Persuasion +9, Stealth +6
Immunities: poison; poisoned
Senses: blindsight 60 ft., darkvision 120 ft., passive Perception 22
Languages: Common, Draconic
CR: 15 (XP 13,000)

Traits

Amphibious.

The dragon can breathe air and water.

Legendary Resistance (3/Day, or 4/Day in Lair).

If the dragon fails a saving throw, it can choose to succeed instead.

Actions

Multiattack.

The dragon makes three Rend attacks. It can replace one attack with a use of Spellcasting to cast Mind Spike (level 3 version).

Rend.

Melee Attack Roll: +11, reach 10 ft. 15 (2d8 + 6) Slashing damage plus 7 (2d6) Poison damage.

Poison Breath.

Constitution Saving Throw: DC 18, each creature in a 60-foot Cone. Failure: 56 (16d6) Poison damage. Success: Half damage.

Spellcasting.

The dragon casts one of the following spells, requiring no Material components and using Charisma as the spellcasting ability (spell save DC 17):

At Will: Detect Magic, Mind Spike
1/Day Each: Geas

Legendary Actions

Mind Invasion.

The dragon uses Spellcasting to cast Mind Spike (level 3 version).

Noxious Miasma.

Constitution Saving Throw: DC 17, each creature in a 20-foot-radius Sphere [Area of Effect]|XPHB|Sphere centered on a point the dragon can see within 90 feet. Failure: 7 (2d6) Poison damage, and the target takes a -2 penalty to AC until the end of its next turn. Failure or Success: The dragon can't take this action again until the start of its next turn.

Pounce.

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