Hell's Precipice

In Normal Mode I did H/H it: Take a healing Hero (Tahlkora for me, Mo/E with "Ward against Elements" or what it is called . . .), a ranged hero (Acolyte Jin, stocked with Savage Shot and Favorable Winds), Jora (any attack skills to increase damage and use Adrenaline; she will never run out of it during fights), Mhenlo, Lina, Devona, and a fourth Henchman. (I took Cynn because she'd taken me through the game so far. Bad choice, you can probably use Durham better)

The wiki has good advice on it, largely the order in which to take things down. Sparks MUST DIE QUICKLY because they can nuke you back to the lobby quickly. Burning Titans are next, because they inflict AoE burning on your people. From there, pick targets and go; if you kill a Risen Ashen Hulk you MUST clear the Hand and Fist which spawn before making more come out. You will regret it otherwise.

Bonus is a crapshoot getting to the Seer in time. Sometimes the Titans charge in and lay the smackdown so fast you can't save the Seer. Othertimes they completely ignore it. Regardless, it doesn't change the approach to the mission at all. Once you get to the portal area, do not try to engage until the Fist and Hand spawns have stopped walking out of the lava. For bonus points, camp in a spot and pull them as they spawn . . . it may make it easier later. Once you're done with the spawns, move in and single out groups one at a time like you've been doing. Portal Wraiths must be taken down once engaged. They're nowhere near as hard as Sparks.

(Bring Signet of Capture. Trust me, you don't want the opportunity wasted. Or you can re-run the mission if you can get it down pat.)

When you move on, wait for the cutscene, then careful-pull the Sparks. Kill them. If you can get the guardian to stay out of the pulling spot, then slaughter him. YOU ONLY NEED TO KILL HIM, and the other enemies will die.

When taking on the Lich, pay close attention. Dazed helps a lot, but keep your people OUT OF THE LAVA. Flag them near the Bloodstone so they run back there. Focus on downing the Lich the requisite number of times (maximum of six I think) and enjoy your shiny new epilogue area.

Things to remember: Warrior titans are NOT FLESHY. All others seem to be; this means you can inflict Poison/Bleeding on Sparks and Risen Ashen Hulks. Don't bring those skills, though, it might be more worthwhile to focus on Blind/Daze instead. (For the obvious reasons.)

Now:

I'm having problems with it in Hard Mode, generally from Sparks' nuking me too hard. There's a spot just before the run to the lava pools where a Titan boss patrols and usually this is where my attempt ends. Part of this is going to be me trying to figure out a better use for skills on the bar. All the same it's been good for loot; I've got a nice library of Warrior and Elementalist tomes from the Titans' donations.

Did it with my brother a few days ago.

1. Me (Warrior tank)
2. Dunk (Word healer)
3. Tahlkora (prot)
4. Ogden (Word)
5. My brother (Necro ursan)
6. Jora (tank)
7. Pyre (interrupt Winter)
8. Gwen (interrupt)

It's not that hard but requires a lot of patience.

I did this a couple of days ago, just to get the Medallion.

Team:

Me (Ranger, really random build, including a never used Winter and a preparation)
Sab's 3 necro builds, although they might be a bit outdated, since I haven't changed them since last year. The MM was useless for most of the mission, too.
The two monk henchies, fire hench and Mes hench.

Move slowly, pulling where possible and killing the Sparks first. Make good use of calling to focus the idiotic henchies on the same target.

At the portal area, I camped right in the middle (next to the lava, not close enough to aggro the patrols) and killed everything that spawned in the lava. Since the bosses don't come at the same time and I didn't have the bonus active, it was no problem. The most enemies I faced at the same time was 4 hands/fists. Easy pie.

After that, or during it if you don't feel it's exciting enough, you can lure the patrols, one at a time, and stab them until they crumble.

I didn't know about the cutscene thing, so I just skipped it, and pulled Rurik with a flatbow. Pain Inverter him him pretty hard, so he went down quickly.

The lich was a real pain, though. No deaths, but he just moved all over the place, and I had nothing to keep him in place enough to finish him. Consider taking some KD or cripple with you.

From what I remember of this mission in HM, it's not that much different, except that you MUST pull pretty much every mob, and have a tank for the Rurik battle.

The portals section is a good exercise in pulling technique. Like others say. Flag the heroes out of the way and just pull the single titans back to the group.

I think it should be good to note that they fixed Winter, and it actually is worthwhile bringing it for this mission now, if you insist on bringing a fire ele.