When he holds his sword out in front like he's blocking only attack if you have counterattack otherwise he will pound you. Constantly Riku will jump to a side and that means that a sword strike is coming so instead of striking wait and then deflect. He also has an arsenal of dark powers to avoid and watch out for. Riku is even faster now that Ansem is possessing him and will do more damage as well thanks to the Dark Keyblade. This again is a pretty hard fight, but if you're an experienced player it can be one of the most fun because you get to use some serious sword skills. Now ener the Castle Chapel and prepare for a boss fight. Now go around the corner and enter the Lift Stop again. Again fight through the Heartless and flip the orange lift.

then enter the Lift Stop again to get to the High Tower. Head into the lift stop and go up and enter the Great Crest, fight through the Heartless and flip the orange lift. Use the Lift to get on the large platform and prepare to fight. Switch the Orange Lift and then call the blue one down to take up to the top level. Head out to the Castle Gates and fight the Heartless. Once you get all four, just go and put them into the door to continue onward to the Lift Stop. Before jumping down cast thunder on the stone tablet. Next use Red Trinity to push the statue off the top, and finally push the statue to the left to reveal the last one. Then smash the two pots next that are adjacent to the statue. First start lighting all the candles around. You'll be back in the entry way where you fought Riku and you need to find the emblem pieces to put on the heartless door to continue through. Once you've unlocked the door from pushing the Red Button, head inside. Different ones require a different number of turns, so just keep spinning until you get the treasure. You will also find pillars with movable shelves and treasures inside. Grab them and replace them to unlock treasure and the way forward through Hollow Bastion. You will also find these books strewn throughout the Library or on the wrong shelf. Inside you will find Bookshelves with book collections having volumes missing. Your victory will reward you the long awaited White Trinity. Don't be afraid to use your sword techniques either like Ars Arcanum. If you're on level you shouldn't have any issues at all, he will go down quick. This is a very important strategy for Riku because it helps and gets you those precious Tech Points. Riku is fast and fast at attacking, but all his attacks can be parried. You will receive the Keyblade and Donald and Goofy back, and it's time to finally time to beat the crap out of Riku. It will open for you when you try to walk through it and prepare for a Boss Fight. Head to the Gate even though it's closed. Now you can head back to the Castle Gates. When you reach the last switch there will be a Heartless, so cast magic and help beast kill it then release the Switch. You just push the next switch every time you reveal one. It's not too difficult so I'll leave out the details. This part has some switches to figure out how to make yourself a path. Inside is some good treasure and Blue Trinity which is useless to you now, so use magic and Beast to grab the treasure if you want then continue down the hall of the Waterway. Take the bubble through and knock the wall down to enter the dungeon. Then use the Call command on the wall for Beast to smash it. Run across the room, because you can't do damage to Heartless and take the bubble on the right for a save point and treasure. You'll notice the gate is shut, but with your new found Glide ability, sail your way around the gate and take the lift down, also make sure you activate the orange lift control as well.

When you enter the Castle gates section immediately take a right. When you reach the top of the shifting platforms a cutscene will occur, after which you will have the Beast but no Keyblade. There are no heartless and some really good treasure including a set of dalmatians so make sure you nab those. First thing to do is scoop up all the treasure here in the opening way. This is one of the most iconic locations in the entire series of Kingdom Hearts and is one of the non-Disney location. Welcome to the beautifully ominous castle of Hollow Bastion. Boss Encounter timestamps for the video below

Kh hollow bastion map