Well, since there doesn't seem to be any information regarding this mob other than loot, figured I'd post what actually occurs while engaging this target.
1. Entering the room
As you enter the room, you will immediately notice it is full of "adds". These adds consist of four non-attackable Vrex mobs (the Taelosian elf models), 6 ikaav mobs, and 6 aneuk mobs. The Vrex elf mobs are positioned in front of Nysf Lleiv, and the ikaav/aneuk mobs are stationed on the room's side bleachers. All adds are permarooted. Once anyone steps in the room and attains aggro these mobs will start spawning adds. The Vrex mobs will summon golem adds about every ~30 seconds or so. The aneuks/ikaavs will summon numerous ukun pets throughout the event; although the pets do not hit hard and have very little hit points, they can be disruptive to heal casting. You can choose to ignore these adds, but I simply just cleared them out. I killed a few of the golem adds when ever time permitted. Managed to kill off the attackable adds within 3-4 minutes.
2. Engaging the boss
After taking out the ikaav and aneuk adds, I started DPSing the main target. I *think* the mob flurried and wild rampaged (can't really remember), and casted spells that normal ikaav trash used, which were completely trivial. Doesn't really hit for much; minimum hit was around the high 800s and max was around a little over 2300. Most of her hits (around ~80%) were around 900ish (was tanking this mob at around 7500ac with cleric and self buffs). By this time, I had about 15 golem adds, but they all somehow died being riposted. When Nyst Lleiv drops below 20% she starts casting single-target charm spell, which lasts about a minute (didn't catch the name of the spell, I apologize). My 90 WAR was hit by the spell, so I'm guessing it's very hard to resist? My ramp-tank cleric-bot managed to tank all golems and the boss while my WAR was charmed without too much issue (had Vow Of Vanquishing rk.II and Ward Of Retaliation rk.II on the clr-bot, which finished off a lot of the remaining golem adds). The fight lasted around 5-6 minutes.
*Side note, Nysf Lleiv was permarooted as well.*
3. Loot
She dropped two items from her loot table, plus one back-flag piece. The unattackable Vrex mobs despawned within a few minutes after she was killed. Had a very happy level 65 clr-alt bot. :)
Have fun with the event!
The cast:
90 WAR (Convorteum/HOT tier 2/3 geared) - main tank
89 CLR (glowing othni armor, plus stuff from 12th anniversary mission) - extra DPS, and wannabe main tank
89 CLR mercenary (tier 5) - did most of the healing <3 :)
90 ROG mercenary (tier 5) - DPS pumpkinhead lackey :)
Edited, May 24th 2012 10:38am by Braikkarrii

Armguards of Envy
Bloodfire Cabochon
Crown of the Forsaken
Earring of the Starless Night
Scepter of Forbidden Knowledge
Silken Slippers of Discordant Magic
Staff of Shattered Dreams
Suede Gloves of Creation
Wand Harness