Phew, we've finally cleared the floor. This will probably only get harder from here, but we've proven we can overcome tough odds.
In between floors, I want to think a bit about Elena, the previous Chosen. For one, I'm curious if anyone in our party (including Martin) might have run into her, or heard anything about her that hasn't come up already. Given what we've learned, I suspect she's traveled most of the same floors as us. When choosing between an angelic path and a demonic path for the third floor, I suspect she'd choose the former. And the presence of that plant monster near the Fae exit and the fact that Muna's sister lost the bet to Dreg last time means she probably went down through Isalia's version of the 5th floor. I'm curious about her abilities, but what I really want to focus on is who or what could have killed her. She was able to take on armies on her own. Yet somehow poison was able to finish her? Not to mention, this traitor apparently lost several times but won in the end, and is choosing to remain on the top floor. Whoever they are, we'll have to deal with them eventually.
It's interesting that no companions were mentioned accompanying Elena here on Calumina. Maybe this companion joined later, so we should ask about them on subsequent floors. But I have another of my patented Crazy Theories so hear me out.
The fact that this occurred on the final floor stands out to me. It reminds me of something Dahlia said, about how Alide wouldn't always be on our side, how she would fulfill her role in the Tower. Don't forget, when Alide isn't in her shop in the floor we're on, she's up in the top floor. So that'd explain why the traitor is staying up there, Alide only leaves for brief windows of time. It would explain the dogged persistence in fighting Elena multiple times before finally overcoming her, if Alide's role is to be the final obstacle a Chosen faces. Given Dahlia was strong enough to kill and replace the Demon of Gifts and Dreg is a former fae king, it would be safe to assume Alide's strength is comparable. It's clear Identify didn't give us everything about Alide, so we don't know what exactly she has up her sleeve. And the idea that the traitor "could only be defeated through death" could be connected to the relationship that seems to exist between Alide and the wandering floor monsters. Although maybe, killing all of them on the first 9 floors could provide an alternative path. Or maybe it's just someone we haven't heard of before and I'm reaching again.
For Yulia alone: Now will be the best chance you'll have for a while to discuss what you've learned about your nature with the others. Whether you share it or not is up to you, but for what it's worth you've all been through a lot together and I don't think they'd see you differently. Also, it would be better to tell them now when your discussion won't be interrupted by anything, rather than them finding out from someone like Dahlia later.