Wyverns are big creatures in the sky in hardmode.
Step 1: Arch Wyverns
They are the deadliest but also the hardest to kill. There is also a regular wyvern and that one is not as deadly and is easiest to kill. Sorry but I do not have the regular wyvern picture so I will get that to you in the comments below. sorry if this was pretty boring. Please comment or post a picture of the regular wyvern if you want to.