Reduced Threat. A reduced-threat monster takes a −2 penalty on attack rolls (included in the stat block), ability checks (included in the stat block for skill proficiencies), saving throws (included in the stat block for saving throw proficiencies), and saving throw DCs (included in the stat block).
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) piercing damage.
Claws. Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit:13 (2d8 + 4) slashing damage.
Stinger. Melee Weapon Attack: +7 to hit, reach 10 ft., one creature. Hit:11 (2d6 + 4) piercing damage. The target must make a DC 15 Constitution saving throw, taking 24 (7d6) poison damage on a failed save, or half as much damage on a successful one.