Just sent in a correction to the upper level limit (was stated as 23 as of this posting) as I had a few of these con light blue to me at 40. That should put the upper limit at around 28.
A warning to any casters out there, these things have an insane regen rate. I had 1 down to a sliver of life but went oom. It was rooted and it regened to 1/3 life before I could med up enough mana for 1 more blast. Everything in this zone seems to have relatively low HP's but this same increadable regen rate. I wish I could get that regen for my mana.
I was hunting here and rooted mob by door (from Netherbian Lair) out to zone proper, mistake as mobs have pathing just outside the door and have no problems getting angry enough to jump in and help out their rooted buddy. So i did the smart but cowardly thing and ran for zone and just zoned out and immidiately in again in hope that the adds would have dropped off and i could finish off the rooted one. Sure enuff the adds where gone and the original target still rooted (took me about 40 seconds to zone out and back in) but it's health had gone from next to nothing left when i zoned to about 90%. So mobs here do have insane regen rates.
These things do have insane HP regen rate. If you plan to exp here, make sure you or your group can finish up the mob, don't let it sit there and regen it's HP.