Okay, Data Xemnas defeated. I have the silver crown. I decided to try to defeat the Mushroom XIII even if I don't enjoy that, just to have the gold crown. It's probably the last time ever that I'm playing KH2.
Man, those loading times were atrocious, especially because the Retry feature seemed to have become standard since BBS. I really hope they put it in every new game in the series at this point. Having to deal with 20 seconds loadings (counting the fact we go back to the previous screen, so there are 2 areas to load and a cutscene to skip, usually) when you are trying your best to learn the boss patterns is a deal breaker. I managed to get over it, but now I'm sure I'll never do that again.
EDIT: I was very lazy and decided to use a guide to defeat the Mushrooms. It's done. Birth by Sleep video unlocked
I have played enough Kingdom Hearts for a while, after more than 100 hours in 1 month (counting both games)!