I just managed to finally finish Hell difficulty on my solo, non-twinked Blizzard Sorceress.
In case you don't know what I was doing, I was playing this sorceress completely solo, meaning no outside help of any sort, not even items. The only items that I had were items that were self-found. I got pretty darn lucky on drops, though, but I did do a LOT of hell meph runs. My lucky drops include an SOJ, occulus, a wizard spike early on, lots of MF gear (chance guards, goldwrap, war travs.) I also found a few things that I didn't get to make any sort of use of, such as 2x Andy's Visage, 2x facets (one lightning, one fire,) some nifty small charms, a gheeds, an Ali Baba, and numerous other things.
I believe, off the top of my head, that my gear at the time of killing Baal was:
Occulus, Spirit Monarch, Atma's Wail armor, Tal's helm, SOJ, Nagel, Chance Guards, Goldwrap, War Travelers, and a rare +2 sorc skills ammy with some MF on it (it might be +1 skills, I can't remember, it's not a great ammy.)
My merc had The Reapers Toll, Corpsemourn armor, and stealskull helm.
Both of us were level 78, and I had max blizzard, max ice bolt, max cold blast, ~15 points in cold mastery, and the rest were 1 point wonders. The only method of dealing with cold immunes that I had was to either let my merc kill them or park them somewhere/leave them.
As far as challenging spots, most of normal was smooth sailing, other than the normal low-level challenges like not having much mana and such. Once I finished normal, I killed normal baal for a while until I was ~40. At this point, I tackled nightmare. Nightmare was pretty easy as well. As a matter of fact, it was so easy, a lot of times I didn't bother "clearing" anything. I don't think I gained more than 5 levels until I got to mephisto. Once I got to mephisto, I killed him for a long long while until I had some pretty decent gear. At this point, I finished up nightmare. The rest of it was easy, and once I got to baal, I did nightmare baal for a long while until level ~60-65. Here, I started act 1, and realized that my mercenary couldn't kill SHIT, and I couldn't do anything to the cold immunes, so I decided I needed a bit more time killing baal/meph to get gear. Eventually, I realized that leveling up and getting mediocre gear in nightmare wasn't going to help much, and struggled through hell. It ended up not being as hard as I had expected, and I got through act 1 pretty easily. Then, I ran andariel for a while in hopes of getting some gear, because I expected that act 2 would be very hard, especially duriel. However, before long I found out that duriel isn't cold immune in hell (I always thought he was) so I took him on and didn't die a single time. Almost all of act 3 consisted of me teleporting to waypoints and hitting the key areas to get khalim's parts. I knew that the high council would be difficult, but decided to attempt to take them on. Surprisingly, they weren't too bad, and with a little bit of effort and separating them, I managed to take them out and get to mephisto.
Of course, at this point, I killed mephisto and realized that my next hurdle would be act 4, specifically the chaos sanctuary. I decided it would be better to kill mephisto until my eyes bled. This is where I geared up, for the most part. By now, I figured that the only extreme challenges ahead of me would be the chaos sanctuary, the ancients, and the throne/baal. I took on the chaos sanctuary. It was pretty damn tricky. In the chaos sanctuary, the Oblivion Knights are cold immune, so the only way I could kill them was to have my merc do it. Unfortunately, they also cast iron maiden, which meant that I had to be EXTREMELY careful, otherwise my merc would die very quickly. I ended up just "parking" a lot of the oblivion knights. The three bosses weren't too bad. Lord De Seis was the only one that ended up being Cold Immune (and I think he always is anyway, because he's an oblivion knight.) My merc took care of him. Diablo was pretty easy, though my merc did die.
This is where I stalled, for a long time, because the ancients were my next challenge and I knew that, since at least one of them would be cold immune, my merc had to be able to take one of them on by himself. Most of my time after this was spent killing Mephisto, occasionally pindleskin, and it ended up being mostly unnecessary. Tonight I decided to finally take on the ancients, and hopefully Baal as well, and found it to be a lot easier than I expected.
I got lucky, and the first attempt that I made at the ancients ended up being a perfect situation, as far as the immunities go. They are mostly random, with the exception of one of them always being immune to cold, and the other two ended up not being immune to cold this time. It was still tricky, since I couldn't put up a portal and I had to make sure that both myself and my merc stayed alive until the end (since I was saving the cold immune one for last.) A lot of quick teleporting around and separating them out led to the first two dying pretty easily. The last of the three was incredibly easy, even being cold immune. My mercenary tanked him and barely took any damage, and what little damage he took he ended up healing with life leech. Ancients were down.
Getting to Baal proved to be harder than actually killing him. I managed to get the waypoint in 3 tries, and then went down to the throne to find that I had an incredibly lucky combination of monsters. There were no oblivion knights or gloams or fetishes. I had to deal with invaders, tomb mages(I don't remember what they're called, but they're the guys from act 2 that raise undead,) and succubi. Only the succubi were cold immune, so I got to the throne pretty easily. I took out the first wave with little trouble, other than Colenzo being cold immune, but he went down fast to my merc. Second wave was probably the hardest of them all, because the skeletal mages were all cold immune (because they are of the cold variety.) This meant that my mercenary had to kill all of them, and I had to keep him alive while trying not to get killed myself. After a little while, they were all dead, and I proceeded. Wave three was pretty easy, but I almost died from hydras since my fire resist in hell was -35. Wave 4 was easy and over with very quickly. Wave 5 was surprisingly easy, since lister was not cold immune, and the minions went down quickly as well.
Baal was harder than I expected, and it took a lot of hit-and-run to take him down. His cold triangle was nearly enough to kill me by itself. After ~10 minutes of hit and run, he went down, and didn't give me anything at all worth keeping. However, my mission was accomplished, and I had successfully beating normal, nightmare, and hell difficulties with no outside help and no twinkage of any kind. Not only that, but I had done what I thought was impossible. I had done it with a single-element sorceress.
Good fun, and a great challenge, but I'm glad that it's done.