Adult Gold Dragon

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.

Fire Breath. Dexterity Saving Throw: DC 21, each creature in a 60-foot Cone. Failure: 66 (12d10) Fire damage. Success: Half damage.

Multiattack. The dragon makes three Rend attacks. It can replace one attack with a use of (A) Spellcasting to cast Guiding Bolt (level 2 version) or (B) Weakening Breath.

Rend. Melee Attack Roll: +14, reach 10 ft. 17 (2d8 + 8) Slashing damage plus 4 (1d8) Fire 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, +13 to hit with spell attacks): - **At Will:** Detect Magic, Guiding Bolt, Shapechange - **1/Day Each:** Flame Strike, Zone of Truth

Weakening Breath. Strength Saving Throw: DC 21, each creature that isn't currently affected by this breath in a 60-foot Cone. Failure: The target has Disadvantage on Strength-based D20 Test and subtracts 3 (1d6) from its damage rolls. It repeats the save at the end of each of its turns, ending the effect on itself on a success. After 1 minute, it succeeds automatically.