This mob is a triggered spawn as part of the evil version of the enchanter quest to get the Illusion Guktan spell.
Took her down with my 58 enchanter, 70 rogue, 70 tank merc (not strictly necessary, ranger could have tanked her with defiant gear/aa's), enchanter pet, 58 wizzie merc -- with all that the fight was over fairly quickly.
Spawn: triggered by a quest turn-in
Loc: roughly pos 800 neg 300 (moves around, I don't have his exact loc)
Level: light blue to a 70 ranger
Difficulty: 300 on chain, solid frequently recast poison, Looooooots of hitpoints.
Invulnerabilities: cannot be slowed, rooted, snared, or stunned, we forgot to try to mez it or charm it but I doubt that you can.
IMPORTANT TIP: Tash the mob. She's crazy resistant to magic...but not after a couple rounds of your best tash. Once tashed she soaks magical dps nicely....wizzie merc charred her to a golden brown. I was also able to land my enchanter dots and dd once she was tashed...did nothing for the stuff she's immune to of course.