Key is to have DPS to wear him down... Beat him with 85 war, 85 shm, 85 clr, 75 mnk, 74 bst and 3 healer mercs. Didn't even need most of the mercs.
Took about 30-45ish minutes maybe but that's because the only DPS was the shaman and warrior during the waves...My bst and the mnk came in by the time this guy was fighting.
85 pally from bertoxx, Soloed the event and fabled version with a tier 5 merc. About 45 minutes to a 1 hour fight. Merc did great with the mana, I had like half my mana left towards the end . The waves of adds at the begining have some fabled tossed in there but they arent bad to kill at all. Dropped 2 fabled robes and 1 ring and other normal loots. My alt is happy with the ring : )......
If The Burrower Beast is up (the untargetable mob back in the cave), the event is ready. Walk into the cavern and shortly you will be attacked by waves of mobs. There's about 6 waves of mobs. After the last wave, you get a LOT of downtime, be patient and watch the untargetable mob. After about 10 minutes, The Fabled mob will crawl out of that same cave and path to the middle of the room. Tag him and kill. No AE's just tank and spank.
If you fail, just leave the room for about 15-20 minutes until everything despawns.
Engrages and Flurries only. Max hit 2995 at 35% shielding, low hit of 620. Approximately 2.5 million hp. Unslowable and immensely magic resistant. Tried about 30 casts of cripple after tashed but it never took.
It sustained 1120 dps on a 77 paladin (3800 ac, max shielding, max avoidance, using 1h shield and sword, 3/6 shield block AA) over 36 minute fight duration.
Dropped 1 Fabled Bile Robe, and 2x Fabled Ring of the Depths in 1 kill.