He can't. That is Riku's keyblade. actually, he can because as long as you're a keyblade master, you can use anyones keyblade. for example, at the end of KH2 when sora killed Xemnas, or when riku gave kairi her keyblade.
Not unless you use cheats.
Sora, Donald goofy and Beast in times
I'm pretty sure that you randomly get when you use different forms ( I got it in the world that never was in valor form)
Don't quote me on this, but I think Sora has to die in a big boss battle. I was watching a Youtube boss battle on KH2 and Sora died and then Mickey came in. He restored Sora and battled a little. A: If sora dies during an important boss battle it will ask you if you want to give up or not. If you say you don't want to give up, king mickey will take sora's place and you can fight with him a little, but what you really need to do is use mickey to heal sora. After that, sora will come back into play.
You know the place where Leon took Sora when you fought Leon? When you were supposed to follow him, you went to a place where there was a little stream of water. Walk through it and use Trinity on the gate.
Go 2 Olympus Coliseum; fight and defeat the Ice Titan in the Gold match (This is in Kingdom Hearts 1 of course; there is no such thing as a Diamond Dust Keyblade in Kingdom Hearts 2 :) but befor that you must defeat Kurt zisa and phantom
Yes you will
In Kingdom Hearts 358/2 Days you can unlock Sora and Mickey as playable charecters. As of now, you cannot play as Diz.
Only Sora
You can not phisically use Riku's "Way to the Dawn", but in the final battle with Xemnas Riku lends Sora his keyblade to finish Xemnas off.
no you play as 3 characters Ventus (Ven) Aqua Terra and its no kh3 its kingdom hearts birth by sleep
No one except Sora Donald and Goofy
Sora, Donald goofy and Beast in times
You can only use Sora, Donald and Goofy, and Auron sometimes
Sora, Donald, Goofy and Jack Sparrow in some times
With Cheats Yes...otherwise (sadly) No
No. There are no codes for Kingdom Hearts 2. You are able to use Mickey however in some boss fights. If Sora is defeated, a reaction command can appear. If you execute the command, you can play as Mickey while Sora heals.
no not really you ONLY get to in the beginning unless you have code breaker and the code