What gave you the notion that it can’t be both?Gotta say, I really like this idea. However, there's one issue I noticed:
If the Flarefin Koi is now an enemy, what will happen to the Inferno Potion, which was formerly crafted with it?
Oh, ok, that's the only thing I was confused about. Otherwise, Hardmode Underworld expansion ftw!What gave you the notion that it can’t be both?
The item may not drop from the enemy, but you can still fish the Koi up as normal. Don’t wooorry about it.
(I’m thinking about going back and buffing some pre-existing Hell stuff after I’m done fixing everything here, actually; Inferno Potion’s on my radar.)