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.

These are pseudo-legendary actions. They can only be used once per battle.

Poison Spittle. Breath attack: The Wyvern roars and showers an area in front of it in toxic spit. All enemies in a 20ft. cone have to make a DC 16 CON save, and are poisened and take 24 (7d6) poison damage on a failed save, or half as much damage on a successful one.

Tail Spin. Melee Weapon Attack:  The wyvern sweeps their spiked tail in a circle. This attack affects all enemies in a 10 ft radius from the wyvern. They must make a DC 18 STR save or take 26 (4d10) 

Call Scavangers. The wyvern knows the gory trail of prey it leaves behind, also attracts it's fair share of followers. A load victorious call can summon a pack of 4 harpies that join the battle as it relectant allies.