Really nice mood in here — the cobwebbed dungeon, the barred door and that big padlock give it a proper creepy, claustrophobic feel, and the top-hat character has a lot of charm even as a placeholder.
The key-hunt + backtrack on limited life, with the timer ticking, is a strong tension hook. Simple to grasp, hard to master — exactly what a trap platformer wants.
One small thing from a level-art angle: since the whole game hinges on precise jumps and reading hazards, it might help to give the traps (spikes especially) a touch more contrast against the dark background — even a subtle warm highlight would make them pop without breaking that gloomy palette. It makes deaths feel fair instead of surprising, which keeps players coming back.