|Completed all of the bonus games and got 100%, unlocked sound test, boss rush, and bonus rush.|
The bonus rush gives you a ranking based on how well you did. I only saw the "Good" and "Bad" ranking screens.
I got reasonably far on the boss rush. it took a lot of practice to learn how to beat these bosses without an animal buddy and without getting hit. The fish boss was hard until I learned its pattern and then it became easy.. the ice monster boss is easy as long as you are super patient... the sun+moon boss I usually lose more than half my health on. it's just that the damn sun always chooses the worst time to shoot down its stars and makes it hard to avoid. and also I keep getting tricked when they do their formation and it looks like they're going to do it one way but then they suddenly switch sides and do it the other way around.
I managed to get up to the 6th boss once at least, and died there. I could keep going and probably get to the final boss with enough practice, but it would be a huge time sink.