Oh the horror of inverted controls... I think the condition for an uncorrupted version of the stage is asking a lot from the player indeed, from having to get all the collectable and the secret while not dying. I would rather suggest that instead of punishing them with inverted controls they would get a more difficult level instead.
With the criticism out of the way, I really thing the sprites are cute and charming, although some sizes may shift a little it could be tweak to perfection! And the platformer mechanic is quite solid with the wall grab and slide, the jumps don't feel too floaty too!
To sum it up, I really like how the game have solid controls and charming sprite, just the inverted controls and the condition for not getting them is a bit much.