Legendary Resistance (3/Day, or 4/Day in Lair). If the dragon fails a saving throw, it can choose to succeed instead.
Multiattack. The dragon makes three Rend attacks. It can replace one attack with a use of Spellcasting to cast scorching ray.
Rend. Melee Attack Roll: +10, reach 10 ft. Hit: 13 (1d10 + 6) Slashing damage plus 5 (2d4) Force damage.
Combustion Breath (Recharge 5–6). Dexterity Saving Throw: DC 19, each creature in a 15 ft radius of impact point (or in line of fire). Failure: 70 (10d6) Fire damage plus (10d6) Force 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 21, +12 to hit with spell attacks):
At Will: Dispel Magic, Detect Magic, Scorching Ray
1/Day: Hypnotic Pattern
Legendary Action Uses: 3. 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.
Commanding Presence. The dragon uses Spellcasting to cast Dispel Magic. The dragon can’t take this action again until the start of its next turn.
Fiery Rays. The dragon uses Spellcasting to cast Scorching Ray. The dragon can’t take this action again until the start of its next turn.
Tail Whip. The dragon moves up to half its Speed, and it makes one attack with it's tail. Melee Attack Roll: +12, reach 10 ft. Hit: 13 (2d8+4) Bludgeoning damage.
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