I really need help here I have a mythril anvil and adamanite forge just in case I have pretty much all crafting stations so... Help?
After killing at least 1 mechanical boss in hardmode (The twins, Destroyer etc.), a mob called a Red Devil will begin spawning in the underworld. These have a small chance (1.33%) to drop a Fire Feather. You also need 20 Souls of Flight which are dropped by Wyverns spawning in the sky.
Combining a Fire Feather with 20 souls of flight at your mythril anvil will give you the Flame wings.