Brass dragon ancestry: Brass Dragonborn trace their ancestry to a Brass Dragon, granting them a magical affinity for fire.

Breath weapon: When Brass Dragonborn take the Attack action on their turn, they can replace one of their attacks with an exhalation of magical energy in a 30-foot line that is 5 feet wide. Each creature in that area must make a Dexterity saving throw (DC = 8 + Constitution modifier + proficiency bonus). On a failed save, the creature takes 1d10 fire damage. On a successful save, it takes half as much damage. This damage increases by 1d10 when they reach 5th level (2d10), 11th level (3d10), and 17th level (4d10). They can use their Breath Weapon a number of times equal to their proficiency bonus, and they regain all expended uses when they finish a long rest.

Draconic resistance: Brass Dragonborn have resistance to fire damage.

Enervating breath: At 5th level, Brass Dragonborn gain a second breath weapon. When they take the Attack action on their turn, they can replace one of their attacks with an exhalation in a 15-foot cone. The save DC for this breath is 8 + Constitution modifier + proficiency bonus. Each creature in the cone must succeed on a Constitution saving throw or become incapacitated until the start of your next turn.