This is the walkthrough for Atlantica as it is featured in Kingdom Hearts, as well as its Final Mix version. Sora and his friends visit another world on their quest, and despite Sora's worry at drowning in the water, Donald reassures him they won't thanks to his magic. Upon arriving they quickly meet Ariel and her own friends, whom teach them how to swim properly.
Completing the world by sealing the Keyhole also grants you the bronze trophy and achievement Master of the Seas in the 1.5 ReMIX version.
Walkthrough[]
Atlantica is unique due to being completely underwater, which you will have to learn to navigate right away in a short tutorial with Flounder. After finding him several times you have to fight a few Sea Neons. These are weak Heartless native to Atlantica, relying on their tentacles for physical attacks and quick dashes forwards. Due to being underwater you are largely cut-off from most of your standard combat skills and finishers, as well as abilities such as Dodge Roll and Guard. Melee attacks will still be sufficient, but magic can be more effective, especially Blizzara. Hit the white clam afterwards, which serve as the treasure chests on this world, to free Flounder and Sebastian and find a save point.
You can now swap Ariel with one of your party members if you wish. She has average attacks, and a single useful offensive melee attack, but her abilities are primarily focused on casting magic. Other than Aero Potion and Cure Potion she also has Thunder Potion. Follow the trident markers to get where you need to go, exploring the Undersea Valley area meanwhile. Use the corresponding magic of the related color to open the colored clams. Eventually, follow the tridents to Calm Depths, where you must enter and quickly exit the current. Next you will run into Search Ghosts, after which you can use Fire on a nearby sea urchin to create a shortcut to Undersea Valley.
Head to Undersea Cave, where you might encounter frozen White Mushrooms, which when released with the use of Stop end up spawning a Pink Agaricus, which grants loot when hit with a certain number while under the effect of Stop. Swim upwards here to enter the Undersea Gorge, another large area, from where you can easily head to Triton's Palace. Upon entry you will encounter Screwdivers, they are healed by Thunder, and maneuver well underwater, utilizing charge attacks. Head to Triton's Throne, then return to the Undersea Gorge after the cutscene. Sheltering Zones now spawn, which are large versions of the Sea Neons that can split into the smaller variants if slain with a physical attack, but not if slain with magic or a critical hit.
Enter Ariel's Grotto, and make sure to open the Torn Page in one of the three chests hidden among Ariel's items. Ride the dolphin moving aroun the Gorge if you have not yet, then backtrack to the Undersea Valley and ride it again to be taken to the Sunken Ship. Enter the ship, after which the Shark will show up shortly, then go and grab the Crystal Trident from the nearby chest. Exit to engage in combat with the Shark, who is similar to Sabor in that he will randomly appear in a few areas. He has no notable attacks, so simply hit him until he flees, using Aero and Cure as usual to handle the damage. He does have a high chance to drop several restorative items upon defeat. Use the passage leading to the Undersea Gorge, where you can hit a vent to create another shortcut, as well as knocking loose a large chest containing an Orichalcum.
Return to Ariel's Grotto nearby, then approach the trident indent for another cutscene. Now head to Triton's Throne, where en route you shall be attacked by an Aquatank. These Heartless spawn with three Screwdivers holding it up, which it can shoot at you. If the antenna glows it will use a lightning-based attack that can heal any Screwdrivers nearby, it absorbs Thunder itself as well. After talking to Triton Ariel rejoins your party, after which you must head to the Sunken Ship, where Sebastian will push a button hidden behind a shipwreck for you, which removes the large rock next to it, allowing entry to the Den of Tides.
Head right first to find a save point in Cavern Nook, and possibly slot a few Ethers into your inventory, then enter Tidal Abyss, followed by Ursula's Lair.
Ursula bossfight[]
The Ursula bossfight.
Follow Triton's advice and focus on using magic, Fire is the simplest and fastest, on Ursula's cauldron. If left alone she will toss potions into it, creating either damaging currents spread throughout the area, or a barrage of fireballs damaging anything close to it. You will know your magic has an effect when the cauldron starts to glow green, and if continued will end up stunning Ursula. She is otherwise largely resistant to damage, but completely exposed and vulnerable while stunned.
Eventually she will regain her senses and use a powerful spinning attack (she also uses this if you attack her without stunning her), which is best avoided entirely by keeping away from here. If you run out of Magic Points you can use an Ether or attack her two moray eels, Flotsam and Jetsam, for they have a much higher MP-on-hit value than other enemies. They are otherwise not too dangerous and more of a nuisance, but can only temporarily be knocked unconscious.
After hitting her while stunned for two or three times she will retreat, after which you earn the shared ability Mermaid Kick. Mermaid Kick can be used to get around much faster underwater, as well as swim against currents. Exit and re-enter to find another sea urchin, which can be shot as well to force the clam next to it to open. Return to Cavern Nook to save and restore, then head all the way back to the Sunken Ship, followed by Calm Depths, where you can use Mermaid Kick to swim against the current and exit the last passage (opposite the Sunken Ship passage), leading to an unknown area.
Giant Ursula bossfight[]
The Giant Ursula bossfight.
This time you will be fighting a giant Ursula, whose head is her only weakpoint, which can be difficult as a lot of her attacks are used through her mouth. She can blow you away, following by blowing a stream of homing bubbles, which are best dodged by moving sideways. She can start to inhale and try to suck you in, biting you, which has to be dodged by moving away with Mermaid Kick (but often you are too close and too late to get away on time). She can also start to inhale, and then wait a moment, preparing to exhale a powerful beam of lightning, which is best dodged by moving above her (moving away means she can target you).
She will also passively summon continuous blasts of lightning around her, which you can see coming due to the glowing light where they are about to strike, giving you a short second to avoid it. Due to the two mouth-based attacks it is recommended to try and strike her from behind or the sides instead, although she often rotates along with you. Her strongest move is used after she has lost 50% of her HP, and is used when she raises her trident and shouts "This won't be pretty!", followed by a massive burst of lightning all around her. Make sure to immediately flee when she is about to use it due to its range and damage potential. Giant Ursula has the most HP out of any boss so far, but will go down eventually.
Afterwards you earn Thundara and Ansem's Report 3. Head to Ariel's Grotto next to seal Atlantica's Keyhole, after which you receive the Crabclaw, which at this point is quite useful, having both high damage plus one extra MP, at the cost of range. The next world would be Halloween Town (walkthrough), although you can also head directly to Neverland (walkthrough), or back to Traverse Town to pay another visit to 100 Acre Wood after collecting another Torn Page.