Well, if you wish to feel accomplished, I recommend you play on Proud or complete the game 100% on normal XD
You have to play through all of the stories on Proud to get the ending after the final episode. If play through all of them on Standard (Or a mix of Proud/Standard/Critical) you'll have to complete the game 100% in the games you completed on Standard. It's kind of confusing. Just complete the respective criteria for each run-through.
Also, I should mention, once you complete the criteria you MUST defeat the final boss fights again. Otherwise the game won't register that you, in fact, meet the criteria. Sorry you'll have to fight Xheanort again, I'll be doing that too.
" I'm contemplating on starting BBS on either Proud or Critical. "
I recommend Proud for the first run through. Even if you've played KH before, this game is a LOT different. You can't mash X the whole time and expect to win, you actually have to consider what you're doing and when you're doing it. It's kind of a big step forward battle system wise, and the bosses are actually challenging. If you start on critical with no experience, you might get so frustrated your PSP explodes. Seriously. Almost threw mine at the wall at Terra's last battle.
Now, if this is explained in Aqua's story, say that and no more and I'll figure it out. I completed Terra's and Ven's story.
Anyway, after the first battle with Vanitas as Ven, you (finally) get rid of his helmet. Since he's Ven's dark side, you expect him to look like Ven...
...WTF he's Sora with BLACK HAIR! That's the only difference. He's even voiced by Haley Joel Osment. Who voices Sora. W. T. F . Is there an explanation for this in the Final Episode, Aqua's story, or the secret movie? (I'm playing on Proud so I'm bound to see it). Please help me with my confusion (but no spoilers. If you have non-spoiler speculation. Fire away.)
" HERE is a melding guide from GameFAQs. I should note that this guide is based on the Japanese version, so some of the names for the commands might be a little different. "
^^ THIS. I used it. It rocked.
The 3rd Vanitas battle is more of a climax than a real "final battle". It was awesome, though. If you want to own him (seriously own him. Seriously.) get Salvation (Called "Holy Rise" in the guide) and Faith (I believe it's called "Holy" in the guide). They both heal the equivalent of Curaga and deal a sh*t ton of damage.
@RoxasXIII: I have a few tips (I beat this ass on Proud).
-Level 40 was my level when I beat him. The tornado area at the keyblade graveyard is PERFECT for grinding. -Make sure you have good commands. My shotlock was Sub Zero (You can find it in the sewers in Disney Town) it easily took out a bar of health whenever I used it. I also recommend Meteor Smash, Zantesuken, (I had the combo Xehanort used but Idr the name), and Curaga. -It's best to hit him after he tries to land that cheap combo. Counters always put me in screwey position. -x3 Magic Haste and x3 Attack Haste abilities.