It has a total of 4,000 health, and will only spawn after the player has defeated the Wall of Flesh and when the player is at sky level (300+ feet, 500+ feet, and 1,000+ feet on small, medium, and large worlds respectively). Wyverns spawn at the same altitude as Harpies. It seems to spawn lower than this on Blood Moons and in The Hallow. This enemy is a mini-boss, and can be dangerous for players without good armor and defense, as the head can hit an undefended player for up to 90 damage, while the body delivers about 40. This is still dangerous because the Wyvern tends to charge into you repeatedly, and lingering in one spot while it is hitting you can rack up a lot of damage. Multiple Wyverns can spawn in one world.