Ancient Gold Dragon

Traits

Amphibious. The dragon can breathe air and water.

Legendary Resistance (4/Day, or 5/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 (A) Spellcasting to cast Guiding Bolt (level 4 version) or (B) Weakening Breath.

Rend. 17 to hit, reach 15 ft. Hit: 19 (2d8 + 10) Slashing damage plus 9 (2d8) Fire damage.

Fire Breath (Recharge 5+). dex 24, each creature in a 90-foot Cone. Failure: 71 (13d10) Fire damage. Success: Half damage.

Weakening Breath. str 24, each creature that isn't currently affected by this breath in a 90-foot Cone. Failure: The target has Disadvantage on Strength-based D20 Tests and subtracts 5 (1d10) 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.

Legendary Actions

Banish. cha 24, one creature the dragon can see within 120 feet. Failure: 24 (7d6) Force damage, and the target has the Incapacitated condition and is transported to a harmless demiplane until the start of the dragon's next turn, at which point it reappears in an unoccupied space of the dragon's choice within 120 feet of the dragon. Failure or Success: The dragon can't take this action again until the start of its next turn.

Guiding Light. The dragon uses Spellcasting to cast Guiding Bolt (level 4 version).

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