Well I told myself I’d stop reading modules for the night and then I saw yours noting draws from Alien and Metroid… so I stayed up way too late reading it all. It hits all the right beats, I personally tend toward sci-fi horror so this had me engaged fully. I love the evolving monster concept as it grows and becomes stronger and the little hints dropped about the prince’s true nature. Giving people access to create the poison and cure is a great way to allow tension to build while that 1d4 poison saps away your strength. The architecture is cohesive and makes for a working understandable space and gives lots of ideas on how our primary monster might utilize these spaces. Also being drawn by the sound of metal is just perfect. Because I can imagine them tipping over a bookshelf and just waiting to get attacked and nothing… sigh of relief as a coin hits the floor and all hell breaks loose. Just a total bit of confusion for a human beings logical senses of a predatory creature.
Some thoughts I did have were as this is for Knave, having coin values for valuable items that are found would be helpful to know how much experience players gain from gathering treasure in this place aside from what the prince is paying them. Another thing that might be helpful and you may have purposefully left this out is time tables for the evolutions. GM discretion can totally be applied here but if as players we decide to track and hunt the thing instead, a time table until it meets its next evolution would be helpful to know.
All in all though I love it and is definitely a thing I would run, now I just need to find the time to run games :).