Wyvern

Wyverns are large Hardmode enemies that spawn at high altitudes. They resemble oriental dragons, are long and white, and follow the Worm AI.

Wyverns spawn at any lateral map location, day or night, but only at Floating Island altitudes. You will know if the conditions are right for Wyvern spawning if you see Harpies, as both spawn under the same conditions, though Wyverns spawn much less often.

Tips

 * Wyverns attack like Devourers and Bone Serpents, except from above.
 * Fighting Wyverns can be difficult, as they deal respectable amounts of damage, are very fast, and continue homing in on the player almost until making contact, which makes dodging difficult. Try to time jumps so that you're falling when the Wyvern is close to making contact, as the speed of your fall will help you avoid contact. Equip all available jump-boosting Accessories. Gravitation Potion and Swiftness Potion will also help.
 * With the Gravitation Potion killing the Wyvern is relatively easy if you have a bow with Unholy arrows or Shuriken or any piercing effect projectile. Simply wait for him to come for you in the sky and fall to the ground. The Wyvern will follow you in a vertical posture, allowing you to damage him 5-6 times with the same projectile. Reverse the gravity when you see the ground and go wait for him back in the sky. Rinse and repeat.
 * As with any large enemy, weapons that pierce targets for multiple strikes (eg. Demon Scythe, Dao Of Pow, Spears) are more effective.
 * With a long sky bridge and Hermes or Spectre Boots, running continuously in one direction can keep the Wyvern behind you for longer periods, allowing a long-range weapon to be spammed behind you. The Wyvern will still get in front of you often, but this method provides more solid attack time.
 * Using explosive ammo is useful too because of it's splash damage being able to damage multiple segments at once.

Trivia

 * Although the name "wyvern" refers to a western dragon depicted as having two wings and two hind legs, but no arms or forelegs, Terrarian Wyverns are shaped after Chinese dragons in Chinese folklore, called 'Lung Dragons' in Dungeons & Dragons.
 * Because of their color, body shape and general style, Wyverns bear a close resemblance to several dragons from popular culture, such as Haku's true form, from the animated film Spirited Away.