The Ilwrath Avenger is a sinister looking ship. The only thing less comforting than seeing one is not seeing one. The Illwrath delight in torturing their enemies and this shows in their ship design.
The Avenger is about average in terms of speed and manuverability. They tend to skulk around and wait for an opportunity to strike. The best defense, the Illwrath have found, is not to go through the effort of dodging, but to instead allow your enemy's weapons to miss entirely through the inferiority of their targeting systems and the incompetence of their Captains.
The primary weapon for an Avenger is a short-range flamethrower known as the Hellfire Spout. The Avenger's quick recharge rate allows it to maintain a nearly constant stream of flame. Many a crew have been cooked alive (only to suffer an excruciating death immediately afterword when their ship explodes into space dust) by the sudden application of this deadly weapon.
While not a weapon per se the Illwrath Cloaking Field is the signature device associated to their race (immediately following, of course, the various implements of pain they use on their captives). Auto-tracking weapon systems (the Earthling Cruiser Point Defense, the Spathi Eluder B.U.T.T.) are useless against a cloaked Avenger, as are any subsidiary craft (Orz Nemesis Space Marines, Ur-Quan Kzer-Za Dreadnought Fighters), the later of which will head back to their mothership immediately. However, the system is not perfect. A well trained Captain, through use of gravity mirroring (or perhaps by sensing the burning hate radiating from the Illwrath vessel) can dumb-fire his weapon systems toward the empty spot in space where the Avenger should be and expect to find it's all-too-solid silhouette. Also, when the Hellfire Spout is employed the ship returns to being visible. It is not clear if this is a limitation of the system or a means of psychological warfare; the starship melee equivalent of "boo!" One can hardly argue the impact on a crew's morale when an Avenger uncloaks on the ship's stern with Hellfire blazing.