Lordy I can't fathom how you got all this done in the time allotted. Feels super complex and satisfying and balanced. Really great music to fit the theme and interesting graphics with great contrast. Great job!
A mix of knowing the engine really well, using experience on old games, and pixel art. The systems also compound on each other, which adds to the complexity. It was a somewhat happy accident that it all worked well together when I was designing it.