Section VIII on Zeb took her down yesterday with 7 people, 9 toons. Here is what we learned:
She doesn't hit too hard... I think the higher hits were for 480ish but most seemed a little lower. She triple/quad hits and is VERY fast. A slow is a absolute must IMO.
Something not listed here is that she charms. Our MT got charmed in-between stunning her and he took out our backup healer.
She summons... just a little FYI for all those lil casters hiding in the back tossing DPS at her. She doesn't seem to summon as frequent as some mobs I have seen.
We found it a little difficult to only pull her. May want to plan ahead and expect an add just in case.
She had a few more hitpoints for a lvl 66 enchanter NPC than I expected. She seems to me like a Vindi for smaller raids/groups. DPS is a BIG keyfactor in taking her down.
She is very generous with "Drowning Panic" and the AE tash. My MR was about 238 after the tash and I got hit with the drowning panic with no problem it seemed. It may be cold based (ice spell icon) and in that case my CR at the time was about 174.
She and the surrounding mobs showed the following resists: P- no resists seen (2 DOTS) M- a little magic resistant (misc spells) D- (not really used) F- no resists seen (primary nuke for me as WIZ) C- Seemed quite high (tried a couple for S&G's)
Some info on Mistress of the Darkwater. She is a chanter mob, which means she comes in HASTED. Kinda surprised us the first time we tried it. Can take down a 65 warrior quick if you're not ready. Try dispelling her haste for before slow lands.
A force can invis all the way up to her. On the level below her, there's a relatively clear place you can set up camp. Pacify or otherwise split the sirens around her. Edit: the place i'm referring to is where the picture above was taken, coincidentally.
She uses an AE called "Drowning Panic" which doesn't do much damage, but appears to be a slow. She also AE tashes.
Either the melees were slowed badly enough that they weren't generating much aggro, or she particularly dislikes casters because i quickly found her turning to me after only a couple of nukes.
She dropped the ring listed here. I'd like to try her again and see if she drops anything else.
She is fairly simple for a single, prepared, group of 65s, so i would think that lower level groups could handle her as well.