Didn't see this thread! Mentioned elsewhere that I'd done a no-kill run, generally avoiding fights but using KOs to complete quests where some fighting was necessary. (The latter are very few in number, so it's possible to skip fighting altogether if you have some metagame knowledge and don't mind leaving some quests undone.) I think the only "unnecessary" KO I did was on Wyll, who for unknowable reasons turned hostile after the initial goblin raid; after resting off his subsequent head-wound he went back to his normal NPC behaviour. I've since posted a big write-up
elsewhere on the forum.
Overall, I won't lie, a lot of times this challenge run isn't amazingly, er, challenging. At least in principle. If you're avoiding combat, your chances of dying in combat go way down! And you can traipse into the Underdark and wrap things up mostly whenever.
Where things get a little more tricky, though, is if you do
go into combat. Ranged attacks -- lethal. Opportunity attacks -- lethal. Any damage aside from the Knock Unconscious action -- lethal. When it comes to finishing enemies off, or when they just enter into low enough health for it to be risky, you've got to start tying your hands behind your back. So the harpies were a lot tougher, since they could just fly away at their leisure, and in the big gnoll fight I had to deal with archers slowly walking away
during their turns. The fiends! So the fights you commit to become a little trickier.
Aside from that, it's just doing what you can to swing ability checks in your favour or bypass them if possible. Disguise Self is great with the goblins and with the gith, for instance. I got really lucky on this one; I didn't have to save scum much, and the one time I accidentally risked a 20 Target check I just-so-conveniently rolled a 20.