This was fun and more content than I expected in a 10-exit hack, what with the secrets and all. I bumped the difficulty to Standard: Hard since this was too difficult for Normal, particularly for 100%.
A minor complaint is that the foreground sometimes blends in with the background, and I couldn't always tell which foreground objects were solid and which were air without experimentation. If you update this, I'd consider desaturating the background and non-solid foreground objects to differentiate them more. Also, after beating the Koopa boss in the castle and watching the credits, I lost the two extra hearts I had collected so I had to get them again (they were useful for the Boom Boom). It would be cool if they persisted.