You usually see such mobs after major patches, and are usually fixed just as quickly. They are typically invisible control mobs for zone-wide scripts and such, as best as we know. There was one in Lavastorm for the longest time, with no name and no graphic, but could be targetted and attacked. This one seems to have disappeared after several people reported it, probably fixed back to it's correct completely invisible state.
Whoops - posted to wrong mob although I see people posting to Raider Spawner describing mob as Ulthork Raider. Are these two different mobs? I have yet to see a Raider Spawner so can't verify.
Ulthork Raider is a DRU epic 1.5 mob. He spawns with 2 man-o-wars in southwest corner of EW (near Icefang) whenever a DRU with waterproof container zones into EW.
He occasionally drops a Carved Prexus Totem, which is turned in to new Othmir in CS. See Druids Grove epic walk thru for details.
I was in EW helping a 60 cleric friend get a tusk for the coldain prayer shawl quest. I turned, he was dead??? I went over to where he was and then I was dead. Being a mage I have few HP's. I went back to get the bod and got killed again. It happened so fast. Hit for 830 and I was in PoK.
He camped my body for a long time and I was killed a total of 3 times. I was not happy.
I will not be going to EW any time soon. Why Sony decided to put a 64 mob in a 38 (?) zone that is invis, sees invis, can't be seen if you have a see invis buff on and hits for 800 is really beyond me. I think this mob is badly out of place.
Kited him for a while. He was camping someone else's corpse at his spawn point, approx -7200, 4400. At least he went back there several times when I had zoned. Was dark blue and KOS to me, 65 Bard. Sees invis, has no model. Tracked to him and could target him and see his name. He gave chase when chanted DoTs at him. He resisted Frost once about like giants do. Cannot be mezzed by Lullaby of Morell.
He summons and killed me when he finally got a triple hit in for 298, 787, 624. Had hit me before for 624 and 820. Tanik Greskil was not up on any of these occasions. Maybe the raider spawner is what is supposed to spawn the Death Squad when stepped on and is trackable and targetable where it wasn't before. I think something is broken.
Full name of the mob is "Raider Spawner", seems to be able to double for 494. The mob is burried beneath the snow and is able to see through invis. So be careful, you might only see the name tag once it attacks you. Can be outrun with SoW at least.