Mark of the Great Red

Red Scales. Resistance to Fire
Legendary Resistance. Once per long rest, when you fail on a saving throw you may choose to succeed instead. 
Dragon Fire. If you deal fire damage to a creature or flammable object, it starts burning. At the start of each of its turns, a creature burning in this way takes 1d6 fire damage. A creature that can reach the burning target can use an action to extinguish the fire.
Breath Weapon - Fire. When you take the Attack action on your turn, you can replace one of your attacks with an exhalation of magical energy in either a 15-foot Cone or a 30-foot Line that is 5 feet wide (choose the shape each time). Each creature in that area must make a Dexterity saving throw (DC 8 plus your Constitution modifier and Proficiency Bonus). On a failed save, a creature takes 1d4 fire damage. On a successful save, a creature takes half as much damage. This damage increases by 1d4 when you reach character levels 5 (2d4 ), 11 (3d4), and 17 (4d4).

You can use this Breath Weapon a number of times equal to your Proficiency Bonus, and you regain all expended uses when you finish a Long Rest.