Walkthrough:Kingdom Hearts/Atlantica

Just before you enter this world, a brief scene will show Sora being concerned about entering this world, since they will drown if they enter it. Donald then tells him that his magic can allow them to survive. Sora, Donald and Goofy have now become adapt to undersea life as to Donald's magic. Once you land Ariel and Flounder will swim towards you from another area, with Sebastian tagging along behind. Soon you'll be given a tutorial on how to swim, just follow Flounder up and down, then finally Sebastian will move along to self-defense but the Heartless arrive to attack. Ariel leaves the area while Sebastian and Flounder hide inside the oyster. Attack the Heartless to proceed further. Ariel will swim back once the Heartless are gone, then you must attack the oyster which will let out Sebastian and Flounder, and reveal a Save Point as well.

File:Donald AT KH.png

After the small cutscene, you'll be able to put Ariel into your party. Head towards the area where the trident is pointing to which will lead you to the Undersea Valley, head to the right to a red oyster, cast Fire on it to open it and get a Mythril Shard. Now as you'll have noticed chests have now become oysters, red for Fire, blue for Blizzard, yellow for Thunder, and plain white ones which open just by hitting them. Now head to the right again into a small alcove where an oyster is, open it to get a Mega-Ether. Head down from where the red oyster is and you'll find another oyster, hit it to get a Mega-Potion. Now go up and head north from where the red oyster is, there should be two oysters, one on a lower platform and the other on a higher platform. The higher one contains an Elixir, the lower one contains a Cottage. Now head down through the exit to the Calm Depths. Now you'll be pushed off by a strong current, if you don't act in time you'll have to go all the way back from the other end of the Undersea Valley, take the first right as you're sent across the current. Avoid the current flowing upwards and swim away from all Heartless, keep going ahead to the Undersea Cave.

In this map there is an oyster inside a small alcove which contains a Cottage, keep going up to the Undersea Gorge. As soon as you get in, head to the left and go as low as possible to get to a Mythril Shard from a blue oyster. Head to the exit for Triton's Palace but take a left and head to the Undersea Garden and open the oyster there to get a Mega-Potion, now head back to Triton's Palace, defeat all Heartless and stay to the right side of the map, there's a yellow oyster here which contains a Mythril Shard. Now head to Triton's Throne straight ahead for a cutscene. Three Screwdivers will be following the party, but King Triton vaporizes them before they get too close. He refuses to tell the party about the Keyhole, and forbids Ariel from leaving the palace. She swims off with the party following, Triton then suggest he's probably being too strict and that he's just concerned of her safety. Then Sebastian tells King Triton that the Heartless are coming from Ursula's Grotto. Now you're back to playing the party, head back to Triton's Throne and open the large oyster to reveal a save point, save and head to the Undersea Gorge and Ariel will as you to go to the far left bottom to Ariel's Grotto.

Inside she'll show you all the things she and Flouder have collected, you may also notice a trident-head shaped emblem on the base shelf, Ariel suggests to go looking for the Keyhole, she doesn't care about what her father said even though Sora reminds her. There are four chests in this area, one is at the bottom near a clock containing a Mega-Potion, another at the 2nd topmost shelf containing a Torn Page, the 3rd is on the 4th shelf from the bottom containing a Cottage and the last is on the bottom to the right of the first chest containing a Ether. Now head back out as Flotsam and Jetsam appear, in fact this leads up to the next cutscene where Ursula is looking over the progress of Sora and the party, she claims they will never find the Keyhole but that Ariel would prove useful and that she's got the Heartless on her side to aid her. She then exclaims that Triton's day is coming. Now you'll be back in control of Sora, head straight ahead to a oyster that contains a Mega-Ether. Head to the Undersea Valley and defeat all Heartless in the area, then look for the Dolphin here and grab onto it and it'll take you over to the Calm Depths then into the entrance of the Sunken Ship.

Here there are numerous chests here, from the entrance go straight and then drop straight down to find a ship with a broken hull, enter inside to a chest that contains an Elixir, then get out and go up and into the ship, Glut will swim by. Now inside the ship there is a chest straight ahead but forget it for now and go to the back of the ship, there's a chest to the left containing a Mythril Shard, there is a hole underneath the stairs that leads to a oyster containing a Mythril, now head back to the chest that we left and open it to get the Crystal Trident, however Glut will appear as you approach the chest. Now head back outside, you can fight Glut for 100XP. There'll be an exit lower down from the main one, but go to the right of it to get a chest containing a Mythril Shard, now head through the exit to the Undersea Gorge. There's an inactive crater ahead of you, hit it to cause a stronger current, head through it upwards to pop out the large Treasure Chest, open it to get an Orichalcum then head to Ariel's Grotto to the right and swim up to the trident-head shaped emblem for a cutscene.

During the cutscene, Sora places the Crystal Trident into the emblem, however before anything happens King Triton show ups and destroys the Crystal Trident, causing Ariel to swim off crying. He also exiles the party from the World however Sora and his party decide to stay regardless of Triton's ruling. Meanwhile, Ursula tricks Ariel into helping her take King Triton's Trident. Once you're back in control, head out of Ariel's Grotto and once you reach the exit to Triton's Palace a cutscene will play showing Ariel escorting Ursula to Triton's Throne to get the Trident. Swim all the way to Triton's Palace and in a cutscene Triton is shown weak and helpless on his Throne while Ursula basks in the glory of the Trident, Flotsam and Jetsam note to Ursula that the Keyhole is not in the Palace and her exclaiming in shock, however Sora and his party make it back to the Palace but Ursula makes off with the Trident. Ariel rejoins the party determined to defeat Ursula and get the Trident back with Sebastian tagging along, before you go, Triton gives a small hint on how to defeat Ursula by casting magic against her cauldron. Save and head to he Sunken Ship map, defeat Glut to allow Sebastian passage to the button close to the door with the strange glyph on it.

Glut
File:Glut KH.png	HP	STR	DEF	MP R	EXP
	200	22	19	32	100
	Resistances	Weapon	Fire	Blizzard	Thunder
		x1.0	x0.49	x0.5	x1.0
		Gravity	Stop	KO	Other
		x0.04	x0.3	x0.5	x0.5
	Rewards	Hi-Potion (100%) Ether (80%) Mega Potion (30%)
Cast Aero and keep casting Fire at it. Once you run out of MP keep attacking it with the Keyblade. It's only attacks are a bite and a damaging shove, however both attacks can be slightly negated by the Aero shield. Use Potions to heal.

After its defeat, examine the button to open a new passage to the Den of Tides. In this area go straight but then take the right path to get to the Cavern Nook which has two clams, open the smaller one to get a Mega-Ether and the bigger one for a Save Point. Now return to the fork in the previous area and take the path to the right, go straight ahead to the Tidal Abyss then go ahead, defeating the Heartless along the way, to Ursula's Lair.

<tabber> Boss: Ursula I=

Ursula I
	HP	STR	DEF	MP R	EXP
	450	22	19	1	1,000
	Resistances	Weapon	Fire	Blizzard	Thunder
		x1.0	x0.0	x0.0	x0.0
		Gravity	Stop	KO	Other
		x0.0	x0.0	x0.5	x0.5
	Rewards	Mermaid Kick
For this fight you'll need lots of Ethers or you can keep attacking Flotsam and Jetsam for extra MP. Use Fire on her cauldron when it's red and Blizzard when it's blue. When done right she will be stunned momentarily allowing you to land a few combos on her. Once she's gained consciousness she'll twist about her tentacles causing massive damage. Cast Aero for any needed help against her attacks. Use Potions to heal.

|-| Boss:Flotsam and Jetsam {{Template:WKH1SBoss |name=Flotsam and Jetsam |image=Flotsam and Jetsam KH.png |size=200px |hp=60 |strength=22 |defense=19 |mpr=100 |exp=150 |physical=x1.0 |fire=x1.0 |blizzard=x1.0 |thunder=x1.0 |gravity=x1.0 |stop=x1.0 |ko=x1.0 |other=x1.0 |prize=N/A |strategy=They do not cause serious damage however they may take out a large amount of health. They have no extra defenses like Ursula however they get in the way. Defeat them for extra MP in case you run out of Ethers. </tabber>

After defeating her, she'll disapear into what appears to be a portal. You'll then learn Mermaid Kick, which is needed to reach Ursula for the second battle with her

Giant Ursula
File:Gigant Ursula KH.png	HP	STR	DEF	MP R	EXP
	900	22	19	36	1,500
	Resistances	Weapon	Fire	Blizzard	Thunder
		x1.0	x0.49	x0.5	x1.0
		Gravity	Stop	KO	Other
		x0.04	x0.3	x0.5	x0.5
	Rewards	Thunder Upgrade, Ansem's Report 3

After defeating Ursula, you'll be taken back to the palace, where King Triton will tell you that the world's Keyhole is in Ariel's Groto. Head to the Groto (don't worry about the Heartless now, since they won't attack the party now), and then Ariel will use the trident to reveal the Keyhole, ending Atlantica's story.

When you return...

If you want to get a 100% completion, you will need to return to Atlantica to perform Trinity Detect, which can be found in Triton's Palace.