Very polished, but there's so much packed in here that I think the readability suffers a bit.
I do like the boss fight mechanic, but I think there need to be clearer or more straightforward links between what the Tell is, what the consequence is, and how the PCs can Cancel it. (Let us recall stories of player groups being stumped by children's puzzles)
For instance if a Warden uses "Fractured Reality" and says "The air around the black hole seems to fracture like brittle glass, you hear morbid whispering in your mind", then I think most players wouldn't understand that they can "self-reflect/confession/being true to themselves" to prevent the outcome, or that the outcome would be a copy of themselves appearing. I think they would conclude "space-time is being damaged, is about to shatter completely, and we should evacuate".
Whereas if the Tell was "Each character sees that their own shadow is starting to take solid form. They sense all the darkest aspects of themselves slowly turning into murderous reality" Then the consequence - they have to face down their corrupted copy - is much more easily anticipated, and the possible Cancellation - trying to repress or acknowledge the dark part of their psyche, or perhaps physically disrupt the copy from forming - is a bit more readily apparent.