Cool demo so far. Two small quality of life improvements I would suggest:
1. When the screen goes dark and the player has no lava lamp and thus is blind guessing, it can be hard to tell when the cursor is hovering over something that can be selected. I would recommend adding a different cursor sprite when hovering over something clickable so it is easier to tell.
2. When choosing an item, it cannot be picked up until after MatPat's audio has ended. I'm sure this is intentional, but it seems to take a bit to long sometimes to allow the player to pick up items again. I would recommend shortening this time if that's feasible.
Otherwise, awesome demo, looking forward to seeing how this project develops.