Hello! Thank you so much for playing the demo and giving us feedback, as well as reporting the bugs!
Actually, there isn't supposed to be an option to view the "mechanical arms cutscene" in the game map again. Only through the scene menu! The fact that you could've triggered it is a bug itself. Thank you for finding this. It evaded me for countless playtests. :D
I will consider adding more hints for the marble locations!
-Hiccup, writer and RPG Maker dev.