For a while now, I've been playing with a self-imposed challenge: don't use or equip any melee, ranged, or armor item above a certain tier. Higher tier items can only be picked up and sold, or be thrown into traps and doors.
I completed a Tier-3 challenge (with the swarm intelligence challenge) with a gladiator. Then I did a Tier-2 challenge with a sniper. Then I did a semi-T1 challenge, where I allowed a sniper to have a T2 ranged weapon (since the only T1 ranged weapon available to her is not upgradable and not transmutable).
At that point I became convinced that a pure T1 run was impossible. Several comments in my previous posts convinced me otherwise, so I decided to keep trying.
I tried again with a sniper (using a puny dart), and died in level 21. Tried with a battlemage a few times, once dying in level 23. Tried with a warden, and died in level 24, right in front of the stairs going down to lvl 25!
I just tried with a warden again, and this time I was successful! The key was getting a RoSS and a RoH. I had never tried kiting before, but it turns out to be a very powerful technique (but a bit boring). It consumes a ton of food, though, but I was lucky again and scored a horn of plenty early on.
I had a blocking enchantment on the bow (don't love it, but useful). The bow was also enhanced for speed. The cloth armor was enhanced for evasion (since it can't even reduce damage from a mosquito).
I also had luck with the wands, even though I only found three in the entire dungeon. First wand, from the mage in the jail, was regrowth +2. I hate this wand, even though many people love it. I transmuted it and got (arghh!!) a wand of magic missile. Luckily (again!) I found another transmutation scroll and this time I got a wand of lightning (yayy!!).
Later on I found a wand of disintegration +2 and another WoL +0, which were useful to harass enemies.
I wasn't super thorough clearing up every level, especially in the demon halls, but I didn't try to rush through the dungeon either. I ended up with 402 kills, level 29, and all SoU and strength potions.
I'm very happy to finally be able to show that a T1 run is possible (even though it requires a ton of luck). I'm going to take a break from SPD for a while (this time for real, I swear!), but I'll keep reading this forum. I'd love to see reports of others trying similar challenges (and I'll try to answer any questions as well).
Thanks for your reply! I understand it's difficult to say what might have happened without more information. I did drop the scrolls right before I openend the door to the second phase (I was still in the hallway).