Ancient Brass Dragon

The dragon can use its Frightful Presence. It then makes three attacks: one with its bite and two with its claws.

The dragon makes three Rend attacks. It can replace one attack with a use of (A) Sleep Breath or (B) Spellcasting to cast Scorching Ray (level 3 version).

The dragon exhales sleep gas in a 90-foot cone. Each creature in that area must succeed on a DC 21 Constitution saving throw or fall unconscious for 10 minutes. This effect ends for a creature if the creature takes damage or someone uses an action to wake it.

Constitution Saving Throw: DC 21, each creature in a 90-foot Cone. Failure: The target has the Incapacitated condition until the end of its next turn, at which point it repeats the save. Second Failure: The target has the Unconscious condition for 10 minutes. This effect ends for the target if it takes damage or a creature within 5 feet of it takes an action to wake it.