On the successful run, I was a level 80 ranger, raid buffed, about 32.5k hp and 4557 AC, almmost entirely Crystallos raid gear. I had leadership AA's, and no campfire. I went to the second pyramid, west side, bottom floor, but outside the pyramd, and about to fall off. I would shrink, sit and stand repeatedly and move around until I could see his target circle taking aim for AOA. /Tar S would target Slitherer. Attack on, cast aoa, lots of bad boy medicine after being summoned. Kill named as quickly as possible. Loot and scoot with my overthere hammer, or die if it didn't fire off in time. Mob HP's was pretty close each time at 164k, average mobs in the pyramid around 70k to 80k. Mob DPS on me was between 150 or so to 640 (I died on the one with 640 DPS on me, as I had a brain fart and weapon shield had about 12 seconds to refresh). The highest successful run was about 260 DPS on me. It took about five Slitherer kills to get the aug. The first kill rotted because I died to the adds, and could not get back to the corpse with AOA. The next three kills had the shoulder item. The fifth run had the aug. I didn't need to be full raid buffed for killing the ph's. One problem I encountered about 25% of the time was on casting AOA, I didn't get summoned, but did get aggro. In which case, the mobs would warp out of their room to outside the pyramid. I would then run for the zone line. Once there was the four mobs from the room only which followed me. The other times it was an impressive train. Overall, Slitherer spawned about one in four PH kills. He spwaned three times in a row as a streak of luck. I killed the NW 'a shissar reaver' in the room exclusively, so don't know if the other mobs in the room work to spawn the named. You might be able to do variations on this idea to get Slitherer on your own, using your own ideas and class abilites. The plow to his room is pretty long. Slitherer has two adds from the room always, and one roamer, which added about half the time. The roamer is on an irregular patrol schedule. I died a bunch of times doing this camp. But the incredible solo experience actually got me about four or five aa's, and no loss of regular experience. It might be hard to get friends to endure the camp, or even find them as the zone is keyed. Good luck.
loc for this guy is 100% accurate; 2nd temple, far west side, middle room. in fact, it's the room across the hall and to the right of the Obelisks update from the Solt 7 access task. got lucky and got my scale on first kill. the NW mob is the PH. it's always 2 shissar reaver's and a shissar sacrificer in the room. you'll occasionally get a temple patroller pather but if you time it, you'll be fine.
on a 4.7k ac sk with max shielding: max 2761, min 563 and a lot of 1488's. no ramp/flurry/enrage. didn't parse anything unfortunately but i'd say he has a good 3-4x as much hp as the trash