Is there a support banner for this?
Also, just one thing. With this, it will make the chance of getting any of the 3 biomes more different. So, in case your character ever needs something from one of the other biomes, and you don't want to wait to make a new world only for it to be the one you already had, there should be a game mechanic available once one of your worlds is in hardmode where you can choose your evil biome before you make it.
Also, I don't think that there needs to be a new Night's Edge, just make your special sword combine to make the Night's Edge. (Considering the Crimson Sword makes the Night's Edge)
Other than that, this is beautiful.