Did this years ago live and now recently back on a progression server. Had forgotten the fight, much below gives the heart of it but there were a few things not listed (or I didn't see).
3x70 mages, 1 enchanter, 2 clerics; Group geared and still wearing mage cast gear on most toons.
Setup: First off, there's no need to clear anything. Invis'd on the run from the Spirit (quest giver) but really there's no need for that either. Skirt the edge of the zone and run over. Go around the thistle cage to the back side. There's a nice flat spot with a fair opening in the thistle around back. Set up there. Not even the door guards will come.
Phase 1: Everyone but the tanks can sit outside the cage, no mobs roam through the area and it's OOR of his AoEs. Damage will be melee only, range melee (arrow, daggers, axes, shurikens) will take no damage. If you have more than one tank you'll have to occasionally HoT the offtanks and likely CH the main. Chanter was able to Tash for both our kills on the first cast. If you're using pets for tanks (we did: 66 air pets), the pet cast spells hit but for usually for 20-50% of typical). The hound is over 200,000hps so this may take a while. We had three mages and all three chained Pyrien Skin on the pet that had agro (at this writing, PS = 4 strike, 482 dmg per strike DS).
At 10-20% health jumps back to 100% and begins Phase 2 (saw no emote for CH nor the like but his health goes to 100%). [For a point of ref, @ 547 DPS this phase took us 7:01.]
Phase 2: Standard fight, we slowed and applied both cleric marks (reverse DS and healing DS). Put a couple HoTs on the pet tank during the entire 2nd phase so he's pretty wimpy in this phase. Clerics DPS'd. [This phase took 2:40 @ 1440 combined DPS].
Entire fight was 10 minutes and 1 second.