The Greenmist was precisely that...a green mist that brought a disease that only affected the Shissar. It was a curse from the gods intended to eradicate the race.
The only way to survive was to go to places where the mist couldn't follow--places where there was no air at all. Hence, The Grey...it has no atmosphere.
If i remember correctly from lore, the Shissar were planning to take their war to Norrath and wipe out the combine, before they were driven from even their lands by the Greenmist fo the Gods. But there was no real time frame as to when this happened. Could it be that the real raiding party that to Luclin to wipe out the the combine were the Shissar, with some of the other evil classes in tow, to tear down the Combine Empire. But, when the people that came to help found no way home and decided to join the combine left behind. While the Shissar went on a seek and destroy mission, to wipe out the Combine once and for all.
Do you have the Ruins of Kunark expansion? Dig out the booklet and read the history of the Iksar. The Shissar were the rulers of Kunark, before the rise of the Iksar empire. (In fact the Iksar were a slave class.
The Shissar upset their gods, in their arrogance and were rewarded with the Greenmist. (Hence, Iksar SK's are 'Crusaders of the Greenmist' and, the high level Iksar SK weapon has a bane effect against Shissar, called, 'Greenmist.
You're really missing a whole lot, if you don't follow all the background and history junk in Norrath.
If this drops off of the mobs I think it does, it is in no way a mid range item... the only named Shissar Revenants I saw in The Grey were yellow to me at level 53! That sounds rather difficult to me. :)
Yeah, but what I think he meant was it can be bought for around 2-3k which is affordable to mid-range players. Also, it'a a cloak that a single group of low 50's can easily get, rather other items it might take a raid of 40+ people.