| Note: Here are the contents of all the treasure chests in the area: Power Up(x2), Defense Up(x2), Megalixir, Omega Arts, Angel Bangle, Three Stars, Dark Ring. Remember that you have to fight a group of Heartless in order to get certain treasures, while you can open others without having to fight anything.
Here just drop down to the end, and climb the vine to your left to get to a platform with a save point. Save your game and jump into the glowing portal. In this area, just go through the portals -- these take you to the worlds that you visited all throughout the game. Each area contains a treasure.
When you reach 100 Acre Wood, save your game and leave the area. Outside go through the portals once more, and you'll be taken to a new room. In this area, there's a treasure chest somewhere near you. (I forgot what's in it.) Now go into the next room and open the treasure chest for a Megalixir
. Examine the panel up ahead for some info. Defeat all the Heartless that appear and leave the place. Outside, jump into the whirlpool for a boss fight.
Boss Battle - Winged Demon
This battle shouldn't be too hard. Cast Aero on yourself first then fly in and attack. Having an accessory that reduces fire damage helps too. He'll start using a devastating flame attack at you after a while, so just fly away from him when this happens. Keep your HP high at all times.
After the battle, you'll get the shared ability Superglide
. Go inside the volcano and fly all the way down to the bottom. Go through the white portal. Do the same in the next 3 screens. You'll be in a huge open area, where you have to fight a Behemoth. After the battle, go through the heart-like thing.
Here, open the treasure chest for a Megalixir
. You'll also encounter your FINAL save point. Make all the necessary preparations, such as having nothing but Elixirs in your item inventory. Once you're ready, save your game and go through the door. You'll be back to Destiny Island. Here, go to the Secret Place for a short cut-scene. When you regain control, go to where Riku is standing, and there'll be another cut-scene with Ansem. He'll fight you after that.
Boss Battle - Ansem
I entered this fight at level 45 in my first game, and believe me he's extremely hard. On my second game, I fought him at level 75 and he became really easy. Anyway I strongly recommend that you have both the MP Rage and MP Haste abilities here, since it's going to make things a little less complicated for you. Also make sure that your partners have a decent supply of Ethers with them, just in case you run out of MP.
Now cast Aero on yourself as soon as the battle begins. (Recast the magic immediately once it wears off.) Ansem will be flying all over the place, thus making it really difficult to hit him. But luckily he does stop and take a break from all the flying. When this happens, Superglide towards him and hit him with all you got. When he uses his guardian to block, attack from the side or back.
Another thing... once he says "submit", get away from him immediately to avoid being grabbed by his guardian. You really wouldn't want to be caught, because in addition to the damage, the guardian will follow you around and Freeze you in place. Just keep a close eye on him and heal when necessary. He should fall after a while.
After the battle, you'll be given a chance to restock on items. So make any necessary preparations, since you'll be fighting the next succeeding battles ALONE. When you're ready, follow Ansem to where he went.
Boss Battle - Darkside
This guy just doesn't give up does he? Anyway, cast Aero on yourself first then attack. He'll start releasing Heartless after some time. Be sure to kill some of them for the HP balls, since you would want to preserve your MP for later. When black heat-seeking stuffs begin falling from the sky, just Dodge Roll to avoid them. The battle will be over soon enough.
Boss Battle - Ansem
This battle will be a lot more difficult than the first, since you're all alone. Cast Aero on yourself as soon as the battle begins. Also he has a new charge attack, but other than that everything else is the same. The strategy for the first battle still works here too. When you hear him say "Take this!", use Superglide and hold the Square button to stay aloft until he stops. Feel free to use an Elixir or two, but not all! This will no doubt be a long and tough battle, so don't get frustrated and you'll win.
You can also stop his charge attack by parrying him, right before he hits you. You'll also get 199 Tech Points for every successful attempt.
You think the battle's over? Well... the answer is no, NOT YET! That's why I told you not to use all your Elixirs. After a short cuts-cene, you'll have to fight Ansem. (again!)
Boss Battle - Ansem
You finally get to fly again. Cast Aero on yourself first, then fly in and start smacking him. Don't hesitate to use either Ars Arcanum or Strike Raid on him too. Try to avoid the lasers as much as you can, since those can inflict more damage on you than Ansem himself does. He'll also blow you away pretty often, so just fly in again when this happens.
When it's over, destroy all the laser-shooting things located below him. Once they're gone, go near the Ansem and go through the multi-colored portal -- the Portal of Darkness. You'll meet Goofy in here. Fight off all the Heartless, and destroy the target at the other end to be taken to the next area. You'll have to fight another monster. Just attack the eyes, and once it's defeated go into the mouth.
Now Donald's in here. Fight off all the Heartless, and collect those MP balls to refill your MP. Destroy the target at the other side to get out. Here, just fly into the mid-section and destroy the heart. It's time to get rid of Ansem once and for all. Just use the same strategy you did before, and now that you have your companions back with you, the battle shouldn't be that hard.
When you regain control after the short cut-scene, keep going forward while picking up treasures along the way. You'll eventually reach a cave with a save point. Save your game and continue on until you reach the end where you need to battle a Behemoth. You'll be taken to the next area when you win.