Turbine's official Dungeons & Dragons Online website has been updated with a fifth monster profile, this time detailing the Iron Defender. Once again, concept art of the creature is included, but you'll need to be a member of the game's forums to view the article. A snip:
In combat, the iron defender relies almost exclusively on its bite, using a mouth filled with blades of serrated metal. In Xen'drik, the common variety of iron defenders has been upgraded; a small pouch just behind the iron defender's mouth can spew out a layer of slippery grease out before a foe. This grease possesses most of the properties of the well-known arcane spell, and it is quick to evaporate. While it lasts, however, all manner of creatures must tread carefully lest they fall to the ground, and become infinitely more vulnerable to the defender's bladed teeth.