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 16 Constitution saving throw, taking 24 (7d6) poison damage on a failed save, or half as much damage on a successful one.

Draconic Breath (Recharge 5-6).  Once per day, the greater wyvern can exhale a breath weapon in a 60 foot cone. Each creature in that area must make a DC 16 Dexterity (or Constitution for poison damage) saving throw, taking 44 (8d10) acid, cold, fire, lightning or poison damage on a failed save, or half as much damage on a successful one. 

Draconic Resistance. The greater wyvern has resistance to the damage type of its draconic origin. 

(Both breath weapon and resistance must be the same damage type).