Note: If you're looking for help with Heroic Mechanar, check out my Quick Tips post.
Made two more runs through Heroic Mechanar the past two days.
First group consisted of myself, a protection warrior, warlock, druid and rogue. The druid dropped out early and was replaced with a priest. Learned some tricks for skipping past a number of pulls at the front, and also learned that Capacitus' polarity charges can be used to your party's advantage. If two players of the same polarity stand together, they get %100 damage bonus!! Knowing that makes the encounter much easier.
I also was witness to the ways in which a good warlock can tear up the demon groups. The guy we were with could almost solo them by taking control of a bomber, banishing another and then healing the bomber as he took care of the other demons.
We didn't even try Sepethrea. And for the waves of attackers after her, we would run down the elevator between most combats. Pretty cheesy tactic, IMO, but you have to be really coordinated to keep crowd control on the Blood Elves as they're rushing you, which is not easy with a pickup group. We muddled through and downed Pathaleon on the first try (I think. Maybe it was the second. Either way, we didn't spend too long on it). Came out of the adventure with 4 badges, but rolled a lowly 1 for the Primal Nether.
Similar setup today, but with completely different players. Had a shaman along as healer instead of the priest. Had a little trouble with a patroller add, and then failing to interrupt Gyro-Kill's Shadow Power buff. First attempt at the Mechano-Lord saw the shaman falling first. We then fought on for another 10-15 seconds while urging the shaman to ankh, but he instead waited until everyone was dead. Second attempt went more smoothly. Skipped the Nethermancer, only ran from two of the event waves, and then killed the Calculator after two attempts. It seems like you really need to kill that first wave of elementals. If you try to just fear them, you get screwed when the second wave appears. Eight arcane elementals auto-firing 1.2k damage arcane bolts is just too tough to deal with, especially when any that aren't feared are likely going after your lone healer! Only two of us rolled on the Nether and I won (just two more to go)!
But this group decided to make a single attempt on Sepethrea. We started off well. I didn't have any of the elementals after me, so I was able to unload on her at the beginning, but then it just got out of hand. I have to agree with those who say this encounter is overly difficult. It's enough of a pain to have to run away when the elementals are after you, but then they can daze you, the Nethremancer can disorient and freeze you, and with three of them running around, you often have to run through some of the flames anyway! Definitely not an encounter that supports melee, which seems to be the case for too many dungeons (auras, AoE blasts, AoE fears...)