The Leviathan that Arkus uses in 'The Silent Legion' is pretty damn awesome. You know the one, black sword with a purple glow in the middle. Sadly, that weapon is unusable, yet the texture for it still exists in the code.
It is referred to as the 'Fallen' reskin. Here's a suggestion: Allow this to be used as a weapon, if not a reskin. The Leviathan reskin is just sitting there, you can make so much with it's potential. Even if it was just the same damage stats as the Leviathan, I would still love it. It won't be too difficult to make it a weapon, right?
You know, it might even be pretty neat if it was a cold iron vanquisher reskin, but with a fiend damage bonus rather than an undead damage bonus. It'd be similar is usefulness, but would make a bit more sense.