Draconic Stinger. The Wygon shares elemental affinity with its dragon parent. Its stinger has 5 charges. When the Wygon makes an attack with its Stinger, it expends one charge to deal elemental damage associated with its draconic heritage. It regains 2 charges for every 1 hour of rest it takes. If no charges remain, the stinger deals only piercing damage. 
Brass, Gold, or Red - Fire damage
Bronze or Blue - Lightning damage
Copper or Black - Acid damage
Silver or White - Cold damage
Green - Poison damage
Amethyst - Force damage
Crystal - Radiant damage
Emerald - Psychic damage
Sapphire - Thunder damage
Topaz - Necrotic damage

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: +8 to hit, reach 10 ft., one creature. Hit: 12 (2d6 + 5) piercing damage.

Claws. Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 14 (2d8 + 5) slashing damage.

Draconic Stinger. Melee Weapon Attack: +7 to hit, reach 10 ft., one creature. Hit: 12 (2d6 + 5) piercing damage. The target must make a DC 15 Constitution saving throw, taking 25 (5d8) poison damage on a failed save, or half as much damage on a successful one.