I have successfully completed a solo and ironman challenge of the entire BG saga with SCS and Ascension exactly once. I did it with a wildmage. For the final battle, I did not have Balthazar or Bohdi on my side. I will add the caveat that I was using aTweaks PnP Fiends, which makes demons/devils far more powerful by giving them their PnP stats and abilities. In some ways this is a buff because the PC can summon them. It's also a double edged sword, because so can enemy mages. The demons you start encountering in game are also far more dangerous because of it. It's mostly a buff until you get to Underdark. Then that sword starts cutting both ways. You certainly cannot spam them at the throne battle, because Amelyssan being a quasi-deity can no-save seize control of them. There is a neat trick you can do though. Summon demons with a projected image/clone, then imprison them. When the time is right, cast Freedom. You'll drop a swarm of demons on the battlefield all at once. Just makes sure you don't mix your fiends, otherwise you'll just import the Blood War and they'll only battle eachother. I accidentally quasi-soloed SCS Ascension throne battle in ToB with a Cavalier. My party got absolutely wrecked immediately. If I recall correctly, the Fallen Planetar with arrows of slaying and Amelyssan with arrows of dispelling machine-gunned through my party in a couple of rounds. I think I had Balthazar bro'ing out with me though. He is pretty powerful, but mostly in that he's extremely tanky. He did die eventually. What helps in Ascension is that you get special abilities from absorbing the pools of divinity. The greatest challenge with ascension throne battle is surviving the first wave against the simultaneous Five. *One more thing. The faster you drain each pool of divine essence, the less time Amelyssan will have to power up. I don't recall on a technical basis what the advantages are, but she is noticeably easier to defeat. It's important not to dilly-dally after defeating the pool guardians, despite the urge to recooperate. It's still one of the hardest battles in all of RPG in history, and probably the hardest. BG2 has several battles that can lay that claim--even just vanilla, with no Ascension or SCS. Twisted Run is one. Demogorgan (especially with Ascension) is another. Draconis is brutal. Various Liches and dragons. Sarevok final battle. So many good fights. Too many to recount without just listing off half of the saga.