Really good all around. As written, the only thing I struggled with was visualizing the mountain itself. I see "Looming in the upper tunnels, [Rinkrank] calls out in a gurgling voice," and, "The PCs fall down twisting tunnels into the Glass Mountain’s heart. Rinkrank’s cottage, a three-room hut with a glass door and three windows, sits alone in a vast glass hollow. It has a bedroom, kitchen, and vault. An old woman sleeps on straw in the kitchen corner." Maybe I'm missing another key phrase, but I'm struggling to understand the physical layout of the Requests/"barricade" situation, to the extent I could explain it to my players.
Is the following correct? There are tunnels inside an otherwise solid glass mountain. Rinkrank's cottage in a hollow clearing in the center of the mountain, which the Players fall into. The Players presumably easily enter the cottage and meet Mani. For some reason, Rinkrank cannot enter the house the same way the Players presumably do, and is instead skulking in the tunnels that are presumably above the hollow clearing, and will drop down once his Entry-seeking behavior is triggered by player choice.
Also, I didn't really understand the Glass Post or who its author presumably is, or why it matters at all for the Players to find. I think that's my own lack of familiarity with the source myths. Is Rinkrank their father? Why is he offering their hand if he's harming them? Is it just to give flavor? Is comprehending it meant to change how the Players act by giving them more knowledge of what lays ahead?
Those notes only came up because this trifold so clearly lays out a flexible vision; great work again! I can't afford Into the Fog but this gives me a really great idea of the "House Style" that Xiao mentions. I really, really like how the impulse to save Bruni in Act 3 rely relies on comprehending that these are the sisters, transformed, which leans into that dawning sense of horror. And the Ever After questions are lovely.