So I'm using the whole Date/Time changing thing to rack up points on the new minigame. See, each song seems to have some sort of a maximum countdown - so setting the date to some time in the past will always reset them to the same times (which are 3h, 8h, 1d). So you can play a song, set the date back then forward a day and play it again all in the "time limit".
Anyway. So the mystery prizes so far have been 1000 bits and a Well (which other people have found and said), and I've just got the third one...
Pffft. I still haven't seen confirmation anywhere that the final is Flash Sentry, but I'll find out soon enough! (EDIT: Oh, I found it. Never mind.) One thing I know for certain is that I'll never manage to get the lyrics to the EG Stomp out of my head.
Another thing I'm trying to get onto is the percentage bonus. It seems completely random but I know my RD keeps a constant 4% so there must be some sort of logic behind it. I know that when selecting a girl it will show first the one with the highest bonus, not including the pony level bonus. So all but one of my mane 6 ponies are at level 5 so they get an extra 10% bonus that the selection doesn't count. It likes trying to give me RD even though she's at level 1 and only gets a 2% on top of her... Song bonus?
It's worth noting that the highest bonus on that selection screen isn't necessarily your best bet.