MM page 303
Multiattack. The wyvern makes two attacks: one with its bite and one with its stinger. While flying, it can use its claws in place of one other attack. Bite. Melee Weapon Attack: +7 to hit, reach 10 ft., one creature. Hit: 11 (2d6 + 4) 2d6+4 piercing damage. Claws. Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 13 (2d8 + 4) 2d8+4 slashing damage. Stinger. Melee Weapon Attack: +7 to hit, reach 10 ft., one creature. Hit: 11 (2d6 + 4) 2d6+4 piercing damage. The target must make a DC 15 Constitution saving throw, taking 24 (7d6) 7d6 poison damage on a failed save, or half as much damage on a successful one.