Your creature type is Dragon, rather than Humanoid.

Your Strength score increases by 2, and your Constitution score increases by 1.

Young wyvern age slowly, but mature quickly. They walk hours after hatching and reach adulthood by 6. They can live to be over 800.

Wyverns tend towards neutral, unlike their dragon cousins who lean extremely to one side.

Wyverns are smaller and lighter than dragons, standing well over 12 feet long and averaging almost 2,000 pounds. Your size is large.

Due to the size and shape of a wyvern's body, a wyvern cannot use humanoid items such as armors, weapons, tools, or instruments. Special Wyvern armor can be crafted, but at five times the cost as their humanoid counterparts.

Your base walking speed is 20 feet, and you have a flying speed of 50 feet.

Due to a Wyvern's size, stealth is harder in most conditions. You have disadvantage on Stealth rolls when walking or flying, unless you're gliding. Gliding takes 5 feet of downward vertical movement for every 10 feet of horizontal movement you move in a straight line.

A Wyvern's eyes are accustom to hunting at both night and day. You can see in dim light within 60 feet of you as if it were bright light, and in darkness as if it were dim light. You can’t discern color in darkness, only shades of gray.

 You have an unarmored AC that equals 10 + your Constitution modifier + your proficiency bonus. This AC can be used instead of your armor's AC.

Your fangs, talons, and tail spikes are natural weapons, which you can use to make unarmed strikes. If you hit with them, you deal piercing damage equal to 1d4 + your Strength modifier, instead of the normal bludgeoning damage for an unarmed strike.

You can use your reaction to inject Wyvern Poison into a creature you hit with an unarmed attack, assuming your tail is used to make it. A creature takes 2d6 poison damage on a failed save, and half as much damage on a successful one. The DC for this saving throw equals 8 + your Constitution modifier + your proficiency bonus. A creature takes 2d6 damage on a failed save, and half as much damage on a successful one. The damage increases to 3d6 at 6th level, 4d6 at 11th level, and 5d6 at 16th level. After using your Wyvern Poison, you can’t use it again until you complete a short or long rest.

You can speak and read Draconic. Draconic is thought to be one of the oldest languages and is often used in the study of magic. The language sounds harsh to most other creatures and includes numerous hard consonants and sibilants.