I've noticed a lot of increased traffic here recently from people doing searches for Heroic Mechanar. I assume they're looking for advice, and while my adventure reports have some useful info, they're not really much of a guide.
So here are a few, quick tips about some of the troublesome mobs:
Netherbinder - I always make these guys the #1 target. Things get ugly if they get a chance to summon their elementals. But with focused fire and a couple of timely stuns, you can easily take them out before they even get a chance to cast.
Tempest-Forge Patroller - They will call for help, so be sure to give yourself some space to fight them in, away from other mobs
Tempest-Forge Destroyer - Interrupt the charged fist! That's by far the most important thing. The cast time on it is extremely quick, so if you have the global cooldown going when they start charging, you will likely miss your chance to interrupt. Generally, I'll open up with a few sunders and debuffs, then I'll just use heroic strike and shield block (since they don't trigger the global cooldown), keeping a close eye out for the charged fist so I can shield bash it. After that, you can throw in a few other attacks before you need to start watching again. Try to keep some sort of snare on him so that if he does get charged, the tank can kite him around until it wears off. It's not really worth the effort to try and heal through his damage while it's charged.
Astromancer - Spell reflection does wonders against these guys. Pretty much all fire damage, so a fire resistance totem would be helpful. Mostly troublesome when they're in the larger groups.
Mechanar Tinkerer - Two general ways to handle these guys. Either have a warlock enslave one and use him to fight the others (very effective) or load up on arcane resistance. With a full suit of Enchanted Adamantine Plate plus a couple of miscellaneous arcane resistance items, I can tank the group of four with little trouble.
Mechanar Crusher - The main thing to worry about with these guys is the disorient effect they will hit your tank with often.
Gatewatcher Gyro-Kill - Keep him turned away from your healers. I *think* his Shadow Power buff can be interrupted. But either way, be prepared to receive some burst damage when he casts it.
Gatewatcher Iron-Hand - Just watch for the 'Raises hammer' message and back off. Any melee shouldn't get hit more than once by the hammer unless they really aren't paying attention. Once he stops, run back in. Pretty easy fight.
Capacitus - Only twist is the polarity effect. Everyone should give the other players in their party some space at the start. After he does the polarity charge, find someone with the same charge as you and stand near them; your damage will be doubled! When he starts to cast it again, move away from everyone else until you can see what type of charge everyone has. Most players seem to like to fight him on the stairs, but I don't see that as a necessary step. His melee radius is huge, so there is plenty of room for everyone.
Sepethrea - Haven't defeated her in heroic mode so I don't have much advice. I would say that fire resistance is required, and if you have equipment that gives you a run speed bonus, this would probably be a good place to put it on! She gets three fire elementals rather than the normal two, and they move at running speed, making it much more difficult to avoid them.
Pre-Pathaleon Event - Very tough. Mainly because you don't have time to designate targets before they're on you. Pulling them back into Sepethrea's room would probably be the best option. That way you have some space, and succeeding waves have to run farther to engage you. Most pickup groups I've been in like to run down the elevator between waves (the mobs wont follow), but that's a pretty cheesy tactic IMO.
Pathaleon - Pretty much the same, though he does seem to be quicker to use his mind control, and the arcane elementals do more damage. Those who are likely targets for mind control should probably use any really nasty abilities they have at the start. This fight is really about dishing out heavy damage as quickly as possible. Once he gets down to ~20% health, his pets vanish and he generally falls soon afterwards. However, unless you have a lot of ways to keep the elementals feared, I recommend killing the first wave of them. It's unlikely you'll get him down fast enough to avoid a second wave, and if you have 8 of them running around spamming arcane bolts at your healer, the fight won't go well.
Basically, aside from a couple of changes to the bosses, everything is pretty much the same as regular Mechanar, only more so. So the tactics aren't that different from a regular run.
For the quickest route, go to the left at the start. You can pull Iron-Hand from Capacitus' area and avoid all the mobs on the right side entirely. Warlocks are not required, but they are helpful. Any Warlock should have little trouble finding a group for Heroic Mechanar. Arcane resistance is useful for the Tinkerers, Capacitus and Pathaleon. Fire resistance is useful for Sepethrea. If you have a single healer, they need to focus their attention on the tank for the boss encounters. Other players should be ready and willing to back off and bandage when needed.
That's about it! This is one of the more popular heroic dungeons and I can understand why. It's compact and fairly straight forward. Pretty easy to acquire four badges (getting the fifth from Sepethrea is tough) and a chance at a Primal Nether, plus whatever other goodies might drop.