I took a months-long break from the game and finally pulled this off when I came back! This was my first 6-challenge win, and doing Doom Slayer gave me 1m+ points as I had planned. It was certainly one of the most stressful and memorable gaming experiences I've ever had!
My humble advice for players chasing the million point badge is, 6-challenge + Doom Slayer is so much more manageable than 7-challenge! You can also do 3-challenge + Doom Slayer practice runs, and if you can get more than 512k points in 3-challenge, the same performance in 6-challenge would grant you 1m points. (1,000,000 ÷ 381% × 195% ≈ 511,811) I was able to get 541k+ in 3-challenge w/ the Battlemage, which was why I believed I was finally ready for this run.
I know the Warden and the Warlock are popular choices for high challenges, but the Assassin's privilege to fight on his own terms (noping out of a sticky situation, getting close to ranged enemies, and later deleting anyone w/ Preparation) was what gave me my first ever win, so I picked him for this formidable task.
The 3 challenges I skipped were FIMA, Pharmacophobia, and Forbidden Runes. (Of course.)
RNG was kind to me. I found a Wand of Corrosion in the sewers and immediately started putting SoUs on it. I think the RoH was found in the Prison. With these two and the Cloak, non-Boss floors posed nearly no threat.
I was nervous even before the Yog fight (I knew victory was close!) and messed up a lot. In retrospect, I probably should've used Potions of Paralytic Gas to freeze the fists and evileyes and what have you and drown them in corrosive gas, but what I actually did was allowing them to get into melee range and fighting them with the Katana while my WoC +9 was sitting idly in my bag. I panicked and even got hit by Yog's death gaze several times, and lost my only Blessed Ankh too.
Some "advanced" tricks that I either didn't know or never cared to use, but had to use for the first time to win this run:
I used an Ankh to reset hunger on Floor 5. I've had a dozen On Diet runs but was never pushed this far. 6-challenge early game is brutal!
I used Stones of Flock for both wand recharging (paired w/ Stones of Shock) and mass damage (paired w/ Scrolls of Psionic Blast) when fighting Yog's fists.
I used Scrolls of Siren's Song during the Yog fight because Doom Slayer can get overwhelming so fast.
I used a Scroll of Foresight during Ascension in the hope of getting some extra Exploration points.
Some memorable shenanigans:
My Shadow Clone was active when I entered a trap room in the Demon Halls. You know, those rooms with many piles of gold, some of them sitting on traps and others on safe tiles. I was collecting the gold from the safe tiles when I suddenly got hit by a Disintegration Trap and nearly died. Turned out the Clone can decide to step on visible traps somehow…
I knew hitting a million points on 6-challenge can be hard so I wanted to reach level 30 for the extra points. I've never had this much trouble getting the two Potions of Experience and spent so much time farming Scorpios that I only had one last torch at the start of the Yog fight.
The Elastic enchantment on a melee weapon takes some getting used to. More than once, I sent a Shaman/Dwarf Warlock/Scorpio flying only to be immediately hit in the face by their ranged attack. (But I do have to say, standing before a door and repeatedly sending enemies away for them to come back to the door for more surprise attacks was so much fun!)
I used an Infernal Brew for the first time during the Yog fight and oh my did it spread! I kept getting lit on fire by my own brew.
Oh and I have several questions too! I searched online but couldn't find any answers. I figured I'll put them here instead of creating a new post.
When calculating the Bosses score (i.e. avoid telegraphed attacks), how does the game evaluate getting "hit" by Tengu's firewall if the player has either a Brimstone glyph or an active Elixir of Dragon's Blood? Do those count as successfully avoiding the fire attack or does the player lose points for it?
Does a prior Curse Infusion grant extra upgrades as the Spirit Bow naturally upgrades? E.g., if I apply a Curse Infusion on a Spirit Bow +4 for it to become +5, when it naturally upgrades itself two times after this, will it become +7 or +8? In other words, is it a good idea to apply Curse Infusion to the Bow right after the DM-300 (or even DM-201 if you're lucky) fight, or should I wait until the Bow upgrades itself to +6 before applying it?