This made me chuckle:

I'm not sure where this came from -- the new dlc or a mod or what, so I'm posting it in general:

 

You're stealing that as we type, right?

 

Now I wonder, is there one of these for every weapon type?

 

I reckon not. Otherwise, it wouldn't be as imbalanced.

 

I don't think that's a core item, I couldn't find that anywhere in core or expansion 2 or 3

 

It's from the More Dred mod. It has a proc that puts a nerf debuff on you.

 

What exactly is the nerf?

 

It pretty much counteracts the stats we see on the weapon, to make it into something more normal.

 

Code:

<spell name="Nerfed" type="self" icon="spells/nerfed_32.png">
    <buff time="90" stacksize="5" allowstacking="1" icon="spells/nerfed_64.png" smallicon="spells/nerfed_32.png">
    <damagebuff crushing="-6" slashing="-6"/>
    <secondarybuff id="2" amount="-6"/> <!-- Melee Power -->
    <secondarybuff id="4" amount="-10"/> <!-- Crit -->
    <secondarybuff id="8" amount="-10"/> <!-- Counter -->
    </buff>
  <anim sprite="sprites/sfx/glintA/glintA" frames="5" framerate="60" centerEffect="0" sfx="metal_drop" />
  <description text="Irritable developers have decided to tweak your stats in response to complaints from monsters that your weapon is unfair." />
  </spell>

Also the icon is PERFECT:

 

Regardless, of the nerf, I really love the concept. Very clever.