Hollow Bastion
You'll start out with no Keyblade, so run or dodgeroll across to the Castle Gates, they'll be closed so save and then go to the lift round the bottom right of the map. When down, go to the right and interact with the switch, it'll turn off and turn on the red switch which you have to get to before time runs out. Now go across the lock-by-Blox thing and then turn right and touch the blue switch, now blocks will fall down and go back up and some will hurt you others won't, so make sure to reach the red switch opposite the blue in time. After you press the red switch, a third switch will open up in the middle, press it.
The doors must've opened by now, go back up with the lift and get through the Castle Gates. Save before going through the entrance, you're now trapped with Heartless, just keep running around and dodgerolling... GOOFY! You'll play a small while with Goofy fighting for you, after the cutscenes go up to the Lift Stop... wait, the door's closed, you'll need to get all Emblem Pieces to open it.
Go to the door on the far right when facing the exit to the Castle Gates, enter and get the Emblem Piece off the table. Go back out the door... DONALD! Go after him, you have two choices out here, you can either explore with Goofy or get Donald. I'll go with the previous, so have him break every block in the area and then attack enemies, then interact with the switch on top of the pile of blocks, you'll have to go over the midway platform to get to the balcony on the other side, so do so. Then go across to the copper platform and get the Emblem Piece, now go back to the lift to get Donald.
First, break all the Blox close to you, then go through to the side with the three switches and let him break the wall of Blox, by now you can see Donald on the other side, but he's trapped. First, interact with the blue switch across the area, forget the Blox Bugs. Have Goofy break the blocks, then touch the lava-like Blox to blow up, you'll get Blizzaga and be able to interact with the red switch. Interact with the other blue switch and have Goofy break the wall for you, on the other side there are more lava-like Blox, touch them to break the rest, then interact with the red switch. Donald is free! He can activate the switch in the Library!
After getting Donald, go to the other end and get the Emblem Piece as well as any other blocks. Use the new lift to get to the Castle Gates. Go in and defeat all Heartless, then proceed to the Library. Examine the dormant switch now and it will open up the bookcase to reveal a way to the next library, go through. In Library 3, interact with the blue switch and get through to the other side and interact with the red switch, now break the Blox on the other end to get to another way for Library 4.
In Library 4, interact with the blue switch, you'll need to use the Ghost Blox to get up and interact with the red switch, however also if can manage to get the Rare Prize Blox, that'd be better. Now go through the new archway to Library 3, however now, drop down to the left side where it is enclosed and go through to Library 2. In Library 2, interact with the blue switch, but keep a good eye so you can get Mega Flare as well as the red switch, after that, you will be able to go to the upper level of the Main Hall. Interact with the blue switch and it'll cause the red switch to light, you'll have to break lots of Blox and defeat 3 or 2 Darkball Heartless to get through, but you'll make it in time. After using the red switch, the Emblem Piece will appear on the middle platform, collect it and drop down.
Now go up to the Lift Stop door and get in to go higher up the castle, you'll be on a lone platform hovering above the Hollow Bastion, fighting Heartless... utilize Spinner Ray as the Overclock meter will always be MAX. Once you land back on the castle, save and interact with the blue switch. Get across the High Tower and get the red switch. Get back to the saving and save, also reequip and commands you changed to potions or anything because a good surprise will happen. Also, get any new commands if you like from the Moogle.
Now, go back, turns out the pipes are a glitch... the Backdoor is on the right side of the middle tower facing it on top of the crest. Go into the Backdoor and defeat all Heartless to remove the pipes. Don't forget that Donald and Goofy will join you this time, so you're limited to fewer commands.
Now go back out, drop down the crest and save, go in and you'll get a new Keyblade, as well as face off Pete.
Boss: Pete I
Pete is pretty easy, just block back his bomb and attack him, the only trouble is when he smacks down to the ground, he'll drop Damage Blox, so look out on those.
Boss: Pete II
Watch out for his new form of attack and movement where he becomes a ball of light and conjures thunder on you.
After this boss fight, Pete will call Riku and you will fight him.
Boss: Riku I
Riku is pretty easy, he won't have any "so-over-the-top" attacks and you'll be able to beat him.
Boss: Riku II
Riku adds a new attack to his deck where he strikes to the ground and summons Damage Blox and one Prize Blox, you'll need to dodgeroll away, however.
Boss: Riku III
The hardest of them all, he will have his Dark Aura command back into him. Dodge roll... QUICK! Because if you don't, you won't make it through.
However, I have found a method that if you do, you'll be able to survive: Stand still and wait for Riku to start his Dark Aura, after he immediately starts it, dodge roll right, then left, then right, then left, then right and then jump. As soon as you land, block and then counterattack.
Once the third boss fight is done, you have finished Hollow Bastion.
