It dropped a piece of Umbracite. It's pretty easy even unslowed, with an ornate geared Pally and Druid. I found it at the second clearing in the left fork of the Netherbian tunnel in UP.
max hit 151, min 47 damage. Once slowed (like all other slowable mobs) these are a piece of cake. They are mezzable if you get adds. Our MA takes about 1100-1200 worth of damage from these so you won't even need to use CH once they're slowed.