Gargantuan Dragon (Chromatic), Chaotic Evil
Traits
Legendary Resistance (4/Day, or 5/Day in Lair). If the dragon fails a saving throw, it can choose to succeed instead.
Actions
Fire Breath (Recharge 5–6). Dexterity Saving Throw: DC 24, each creature in a 90-foot Cone. Failure: 91 (26d6) Fire 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 23, +15 to hit with spell attacks): At Will: Command (level 2 version), Detect Magic, Scorching Ray (level 3 version). 1/Day: Fireball (level 6 version), Scrying.
Multiattack. The dragon makes three Rend attacks. It can replace one attack with a use of Spellcasting to cast Scorching Ray (level 3 version).
Rend. Melee Attack Roll: +17, reach 15 ft. Hit: 19 (2d8 + 10) Slashing damage plus 10 (3d6) Fire damage.
Legendary Actions (3)
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.
Commanding Presence. The dragon uses Spellcasting to cast Command (level 2 version). 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 (level 3 version). 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.
Found on p.256 of MM2025 (Free Rules)