Ancient Wyvern

Keen Sight and Smell. The wyvern has advantage on Wisdom (Perception) checks that rely on sight or smell.

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: +11 to hit, reach 10 ft., one creature. Hit: 17 (3d6 + 7) piercing damage.

Claws. Melee Weapon Attack: +11 to hit, reach 5 ft., one target. Hit: 20 (3d8 + 7) slashing damage.

Stinger. Melee Weapon Attack: +11 to hit, reach 10 ft., one creature. Hit: 17 (3d6 + 7) piercing damage. The target must make a DC 17 Constitution saving throw, taking 35 (10d6) poison damage on a failed save, or half as much damage on a successful one. On a failed save, the target is also poisoned for 1 minute. A poisoned creature may repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.