Multiattack. The magma dragon makes two attacks: one with its bite and one with its claws.

Bite. Melee Weapon Attack: +7 to hit, reach 10 ft., one target. Hit: 17 (2d10 + 6) piercing damage plus 13 (1d8+8) fire damage.

Claw. Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 15 (2d10 + 4) slashing damage plus 7 (1d6+4) fire damage.

Erupting Lava Breath (Recharge 5–6). The magma dragon exhales molten rock in a 30-foot cone. Each creature in that area must make a DC 16 Dexterity saving throw, taking 27 (5d6+10) fire damage and 27 (5d6+10) bludgeoning damage on a failed save, or half as much damage on a successful one.

Flicking Tail. 
Melee Weapon Attack: +7 to hit, reach 10 ft., one target. Hit: 15 (2d10 + 4) bludgeoning damage plus 7 (1d6+4) fire damage. Once per short rest, when a creature makes an attack roll against the magma dragon within 10 feet, the magma dragon can use its reaction to make an attack roll against that creature with its tail.