From what I can gather this is the story:
This is a spawn that takes a week. When Ithiosar the Fallen spawns you can kill him (apparently he is a whimpy dragon only quad hits for 700 etc. Sure as hell would kill me in one tick). When he dies you can loot him for one of many class specific belts (NOT JUST BEASTLORD ones). However his big Brother Ithiosar the Black is downright nasty, and like the corrupted in OOT spawns straight after his little brother dies.
From what I have heard he does not like people looting his brother's body.
Rumour has it that everyone fighting Ithiosar the Fallen have killed him looted and run like hell to the TT zone. They then come back to retrieve the numerous PC corpses.
In other words, bring ya NIKE's people this puppies brother Ithiosar the Black will make you hurt and The Swamp of No Hope is a lousy place to die unless you are an IKSAR like me :)