The End of the World is, like Hollow Bastion, not based on a Disney movie. It is instead formed by what's left of worlds after the Heartless took over. The Heartless here aren't too easy to defeat, and the Behemoth is added as a regular enemy.
You'll be starting in a small cave. Simply walk through the opening to trigger a cutscene. Walk forward for a small scene where the large ball of energy comes down and starts a battle. You'll be introduced to the new Heartless here. For information on specific Heartless, see the Heartless page. After the battle is over and you successfully defeat the Heartless, you'll return to the area you were in before the battle with the Heartless. Here you'll find that opening each treasure chest (or trying to open one) scattered along the side will launch you into battle. This is a good chance to grind, and you can also get a reward from the treasure chest after the battle is over. However, these battles aren't necessary and can be ignored if the prizes aren't desired.
Head into the light all the way at the end of the path and you'll be immediately thrown into a battle pitted against a Behemoth. Defeat it to make it to the next area. This area is large and has a bunch of platforms scattered around. Gradually glide forward, but also let yourself fall until you see a light. Jump into it to move on. Once you make it to the next area, walk into the light in front of you. You should end up in an area looking exactly the same except for a large, dark, vertical beam in the center of the room. Walk into it to be taken to Traverse Town.
After entering the strange light, you'll end up in Traverse Town. Your specific goal will be to wipe all the Soldier and Large Body Heartless out of the third district. Afterward, simply exit through the tall wooden doors to go back to The End of the World. From where you ended up, go forward into the next small light and you'll be teleported into the next area. Another beam of dark light is centered in the area. Walk into it to end up in Wonderland's Rabbit Hole. Here you'll face Red Nocturne, Blue Rhapsody, Yellow Opera, and Green Requiem Heartless. After you defeat all the enemies here, repeat by finding the door, walking into the next light, and then walking into the next beam to end up right outside the Olympus Coliseum. The process keeps repeating with Deep Jungle, Agrabah, Atlantica, Halloween Town, Never Land, and then finally the 100 Acre Wood. All there is at the 100 Acre Wood is a Save Point - no Heartless here. Exit the "world" and once again walk into the light. Instead of the beams as seen before, this one will resemble fire more than dark energy.
Once you enter the area, you'll be immediately attacked by Heartless. Defeat them and then move on to the door, which slides open to reveal a small room. Examine the strange mechanism in the middle for a reading. After you're finished reading, a group of Heartless will attack. Defeat them all and you can then jump through the dark orbs from which the Heartless came. Jump into the large opening in the floor to begin the boss fight.
Chernabog is a demon from the segment "A Night on Bald Mountain" out of the Disney film Fantasia. His attacks are mostly fire-based, his arsenal including attacks such as fire-breathing and throwing fire at the party. Chernabog is also exceptionally large. Fortunately, Sora, Donald, and Goofy have the ability to fly for this battle. Use locking-on to your advantage and try not to stay in view of him. Though his head is his weak point, it's best to attack the back of it instead of the front. Chernabog will occasionally breathe fire, which is an attack that can easily hit you if you stay by his mouth. Beware of a deadly attack Chernabog can cast, as always involving fire - he can make fire surround himself like a barrier. If you get caught up in this while attacking him, this can prove to be a killer - Sora will get so caught up in the attack that he won't get a chance to heal before a Game Over. Another one of the demon's attacks is blowing wind to try to keep you away, but this can't be too harmful. Just fly over it or wait for the attack to finish and then continue attacking. After defeating Chernabog you'll earn the command Super Glide. This is like gliding, but is much faster in general.
After the battle, descend into the volcano where Chernabog was fighting you from. Keep descending the platforms until you reach the ground floor, where there should be an opening filled with light. Walk through it to enter a new area. Keep moving into the light in every new area, until you come onto a green ground where you must battle many Heartless.
Head through the door and you'll end up back at Destiny Islands. Go to the Secret Place to trigger a cutscene. Get ready, because next up is the final boss fight.
Here you'll finally get to face the source behind all the trouble - Ansem, Seeker of Darkness. Unfortunately, Ansem has back-up, and he won't be the only one attacking you. His Guardian will constantly come out behind Ansem's back to attack you, being nothing short of a nuisance. Be sure to lock-on to Ansem though - he's the one you're fighting here. If Ansem goes down, his Guardian will go with him. There's not much strategy here except for battering Ansem with your Keyblade. You can guard and deflect attacks, although this doesn't do much to hurt Ansem's HP. Also an eye on your Attack command. The Guardian can switch it to Freeze at one point, which, if you try to attack with it, will stun Sora. The best you can do here is move around, cast Aeroga, guard, and attack. The best advantage you should have is your Level.
After the previous battle, Ansem will enter a crater he created, giving you a chance to equip healing items or any other equipment to give yourself an edge. Once you enter the crater, you will have to fight Darkside, who has much more health than the first two battles with it, but it's still not a hard boss. Once it is defeated, Ansem will come out, ready for more.
The second fight against Ansem is more difficult than the first. While he has less HP, he has a few new attacks that make him a more powerful opponent. To make matters worse, Sora has no teammates to help him in this fight, which means you're Ansem's only target and must heal yourself when needed. Fortunately, Ansem doesn't fire energy disks in this battle, nor does he float out of your reach, so he should be easier to hit this time around. Ansem himself still commands his Guardian to occasionally block frontal attacks, to physically hit you, and to sometimes change your Attack command to Freeze, which, again, makes the Guardian hold Sora in place, keeping him from doing anything for a few seconds. When the latter is being used, Ansem will periodically create a barrier around himself to attack Sora if he is too close.
As for the new attacks, one move involves Ansem shooting across the arena in order to hit you, causing damage. This attack is always used when Ansem says "Take this!" and it can easily be stopped by either hitting Ansem with your Keyblade, or by using Guard. Ansem's other new technique is only used when about half of his HP has been depleted. Here, Ansem says "My strength returns!" and the scenery darkens, signifying that he's about to use a dangerous attack. His Guardian enters the ground and tries to shoot out underneath Sora, inflicting serious damage. The attack can simply be avoided by moving around the arena, preferably in a circular fashion around Ansem (who will be standing in the middle of the crater at this time, immune to all attacks). When the attack is nearing its end, the Guardian creates a shockwave that shouldn't be to harmful. As long as you know how to avoid all of these moves and keep your health at a tolerable level, Ansem shouldn't be too overwhelming.
After the previous fight, a cutscene will begin, so prepare yourself for Ansem's ultimate form...
World of Chaos
During the battle, Ansem wields a large double-bladed Soul Eater pole arm. The World of Chaos itself can shoot lasers from virtually anywhere in the arena, as well as summon or throw Bit Snipers. Its ultimate attack consists of knocking Sora back and firing numerous lasers that track Sora.
A much larger Ansem has merged with this living Heartless ship, so cast Aeroga and lock onto him. Fly around and inflict damage to him from various angles, much as you did with Ursula and Chernabog. Avoid all the laser beams which emanate from Ansem by flying away and moving up and down. When they’re gone, lock onto him again. Also, watch out for his halberd attacks, as they’re powerful. Fortunately, he doesn’t swing this weapon too often. Taking him out will send you into another part of the ship.
Appearing during the final battle with the World of Chaos, there are three Room Cores that are prisons consumed in darkness. At the beginning of the battle, Donald and Goofy were imprisoned in separate ones. Sora was at one point imprisoned in one, but escaped. Each of them is within a pitch black zone with the Heartless emblem on the floor, filled with Heartless.
These are only able to be attacked by destroying all the Heartless in the room.
- Room Core: Use Graviga to take out vast amounts of Shadows at once. When you beat the last one, a sinewy strand appears in the center of the room. Go after it with a combo to free yourself from the black zone.
- Room Core (II): When the Artillery are eliminated, a portal appears. Fly into it to rescue Goofy. Except for having Darkball Heartless (which drop MP balls) to face and Goofy on your side, this fight is just like the last Room Core battle. Destroy the glowing Room Core itself to get both Sora and Goofy out of there.
- Room Core (III): The defeated Face reveals another portal. Fly in to rescue Donald. This is an easier fight, since your party is back together. The only problem is, you’re taking on a room of airborne Invisibles. Beat them with physical attacks, then attack the red Room Core to exit.
Artillery are Heartless that appear on the World of Chaos. They are bluish organic cannons that are attached to the World of Chaos, and shoot blue blasts of energy at Sora as he flies by. A stronger version of them is also present, called Heavy Artillery. When they are destroyed by Sora, Donald, and Goofy, another set respawns after a certain time, but within the time when they're gone attacking the World of Chaos becomes a more manageable task.
The Face is on the front of the World of Chaos. It must be defeated in order to save Donald, but watch out for its powerful attacks.
A good strategy for defeating the Face is to cast Aeroga on Sora and attack with combos, but keep your MP up to cast Curaga etc. The face seems to be one of Ansem's minions that he summons to his aid in the fight against Sora. The Face will frequently open its mouth and release lightning bolts from the sky that will automatically seek out and strike Sora from above no matter where he is. The only way to dodge them is to glide around the area. On top of that, many missile shooters can harm you, so stay alert. When the Face's HP is depleted, you will have to enter the Mouth of the Face to fight more Heartless and rescue Donald Duck, then you will be able to attack the central energy core of the World of Chaos Heartless.
The Main Core is the "heart" of the World of Chaos, reached after Sora has been reunited with Donald and Goofy. There is not much strategy to this fight. Simply remove the artillery around the area, then hack and slash at the organic mass at the center until it is destroyed. Having the full party makes this chore much simpler.
Aware of the damage the heroes are causing to the World of Chaos, Ansem breaks the seal on himself in order to stop them from destroying it. He has not changed much since the last fight, except for a new, powerful attack that can draw the party in as close as it can, before launching a large explosion.
Simply follow the same strategy as the last battle, cast Aeroga and lock-on.
After the battle, enjoy the ending cutscenes - you've beaten the game.