Lord Rulgax  

I won't find out till tomorrow but the door is labeled To Enchanted Lands. It is the only door left after you kill the overlord. I don't know if it is supposed to say Chamber of Rulgax but it doesn't nonetheless. Do not take the man hole cover, you will exit the instance and not be able to reenter for 18 hours

49 Shadowknight can take him on with almost no problems, drops the Mastermind's Coif of Control about 30% of the time, and its usually with a Rare Tier 3 or 4 Rare.
Have never gotten a master chest off of him yet.

Faced him a couple of times on my Shadowknight (48) He's not too difficult as long as you clear out the add that patrols the circle around him.

Fought him 4 times and he's dropped the Mastermind's Coif of Control twice, and dropped a Ebon cluster and a Oak Root with a Flurry of Blades (Master I).

after LU20 seems SOE "helps" the lord ;) cant solo with 53 nec adept1 tankpet :/
btw it is not a rare monster, zonelock is 18h and everytime lord is up in this instance.

Soloed as a 51 necro with adept1 tank pet without any problems, just one heal for pet required :)

Dropped Master Chest (sorry only german names for the itmes):
Umkippen - Wächter 35 - Adept1
Ruthenium Anhäufung
Schwarzer Treibsand - Illu 33 - Master 1

Been killing Lord Rulgax on my Necromancer alt the last few days, and I haven't been seeing any of the t5 rares listed above - only t4. Feysteel, High Quality Pelt and Severed Oak.

Tonight's take, in one chest, was:

Woven Reinforced Skullcap
Stunning Cry (Adept I)
Feysteel Cluster
Lucky Boon (Master I)
Archons Great Flail

Last night had an adept, and a decent cap:

Mastermind's Cap of Control
Legendary, Lore, No Trade
+10 agi, +10 int, +40 power, +168 vs. magic, +168 vs. mental, +4 subjugation
Mage (40)
Mitigation 82

That cap and the Archons flail are the only t5 items (both level 40) I've seen in the past few days, so it's possible that his loot table's been dropped back a few levels from previous reports.

Once you've killed Baylzuthak, you can clear over to the entrance to Rulgax's chambers.

When you zone in, you'll find a room with a group of 4x no arrow goblins, and a seperate group with 3 eyes, 2 ^^'s and one ^. These were all sorcerors for me. Clear them and the door opens.

On your way down the next hallway 2 occulus soothsayers spawn and agro you, so go slowly. This is the only surprise here.

The rest is linear, 3 more mobs with Rulgax at the end. He's fairly resistant to mental/magic spells, and probably other spell types as well.

Also drops Shaped Ebon Coin.