Okay so I've been thinking on the Dungeon:
Good news! I think we have a genuine shot. There's a number of factors like the dungeon primarily being Essence based (Minus whatever it is Maw does to other sources) and it being situated in a forest (Potential chances to use Accelerated plant growth). We're also able to effectively fight whilst Decapitated, but we shouldn't expect that Durability to save us given that Sly has been implying this will still be a hard fight even with it.
So on the one hand, we can definitely leverage some of our strength.
The Downside? I think we have a decent shot against going up something Sentient instead of just a horde of monsters. This dungeon already seems to be doing way more than "Efficient Tension Sustainment", So I think we can assume that other restrictions mentioned in it are also being ignored. The fact that Sly has also apparently implied that even with where we are right now, such a fight would still be hard is... not really a good sign.
Another possibility that we have to assume that this has way more than just Essence to it. Alectai a while back mentioned it might have levelled up enough to start using Flow, And while that wasn't actively confirmed, we have seen Iterator's beasts use Flow abilities (i.e. messing with our perceptions) alongside some form of space manipulation with the Deer.
And... Well I wouldn't be surprised if we found Jeremy in there. There's implications he's some form of Maw Sublet, and given that Rapid Iterator is dealing with Maw Corruption (Maw seems to work weirdly with other Sources? Maybe it makes things more like itself?) I wouldn't be surprised if the two were connected. Or if it was the same corruption that attacked us at the start is also responsible for Jeremy and Rapid Iterators infection. Expect Maw bullshit basically, so if we have the chance, I'd like to ask Flower about that.
Still, I do think we have a chance, especially if Shine Expands before we go to the dungeon (Which would also net us another Ethos to use). I doubt it will be able to assist us in an offensive capacity, since it's name and description puts the emphasis on Gentleness (though not weakness), but It could still provide a useful defensive function or a buff. Or even potentially a pathway for Aurora to assist if that ends up being on the table (don't count on it though, seems unreliable). In terms of Durability, we're surprisingly high (though lack strong regen in combat) and Pulse surge alone makes for a hell of a combat ability, which can be combined with our precognition to better aid us. Given time, we might be able to do out of combat healing like we did in 2.6 part 2, Combining Hope Shock and our Essence healing, and with Enhanced Metabolisms Second Threshold, we don't even need to be fully healed, just not amputated. Though we will probably be coming out of this looking like we got tossed in a meatgrinder.