Multiattack. The dragon makes three attacks: one with its bite and two with its claws.
Bite. Melee Weapon Attack: +9 to hit, reach 10 ft., one target. Hit: 16 (2d10 + 5) piercing damage plus 5 (1d10) lightning damage.
Claw. Melee Weapon Attack: +9 to hit, reach 5 ft., one target. Hit: 12 (2d6 + 5) slashing damage.
Lightning Breath (Recharge 5-6). The dragon exhales lightning in an 60-foot line that is 5 feet wide. Each creature in that line must make a DC 16 Dexterity saving throw, taking 55 (10d10) lightning damage on a failed save, or half as much damage on a successful one.
RollQuest summary Senses: blindsight 30 ft., darkvision 120 ft., passive Perception 19. Languages: Common, Draconic. Saving throws: Dex +4, Con +8, Wis +5, Cha +7. Skills: Perception +9, Stealth +4. Speed: 40 ft., burrow 20 ft., fly 80 ft.
RollQuest ships the D&D 2014 SRD as a content pack, on a 5e character sheet that does the maths - roll from the sheet and let the numbers work themselves out. Free to start.