http://www.project1999.org/forums/sh...ight=greenmist has pretty much all the info on the subject.
In theory
Greenmist was officially introduced two months before Luclin, was Iksar only till post Luclin, had Space snake bane but no Space snake to bane it on (Wraith of a Shissar isnt tagged one).
How devs will decide to introduce this here I have no idea, but that's how it was on live.