Thank you for the feedback!
"-If you walk into Monsieur Void at the start he just snatches you and the game ends. Ruined my first run in seconds"
This is quite the intended result! Don't bother him too much.
"-Please have mercy on my CPU :("
i am definitely trying!
"-Are there supposed to be keys in the game? The chest wouldn't open without one but I never managed to see one (maybe a skill issue on my part)"
A key will spawn on an enemy, you just have to grab it!
I will definitely make note of the other points too! This isn't going to be a super big game.