The Hundred Acre Wood secret world:
To unlock The Hundred Acre Wood (Winnie The Pooh) secret world, complete the Monstropolis world. Then, return to Bistro in Twilight Town to find Merlin waiting there. He will give you a book that warps you to Winnie Pooh and his friends in The Hundred Acre Wood. It is a very small side world that just consists of one garden. You are supposed to help your friends with the harvest by completing three mini-games.
Successfully complete the indicated task to unlock the corresponding keyblade:
Classic Tone: Successfully complete all 23 classic mini-games.
Crystal Snow: Successfully complete Arendelle.
Ever After: Successfully complete Kingdom Of Corona.
Favorite Deputy: Successfully complete Toy Box.
Grand Chef: Get an "Excellent" rating on all the bistro recipes.
Happy Gear: Successfully complete Monstropolis.
Hero's Origin: Successfully complete Olympus Coliseum.
Hunny Spout: Successfully complete 100 Acre Wood.
Nano Gear: Successfully complete San Fransokyo.
Shooting Star: Successfully complete Twilight Town.
Starlight: Successfully complete the Keyblade Graveyard.
Wheel Of Fate: Successfully complete the Caribbean.
Bonus Gummi ships:
Defeat the Schwarzgeist optional boss with any rank to unlock the Golden Highwind and Schwarzgeist Gummi ships. Defeat the Schwarzgeist optional boss with an "A" rank to unlock the Ultima/G Gummi ship. Note: The Schwarzgeist optional boss is found inside the large green tornado at the center of the Misty Stream Galaxy (second Galaxy you visit).
Ultimate weapon recipes:
Collect 58 different Synthesis items, then speak with any Moogle to unlock the recipes for Sora, Donald, and Goofy's ultimate weapons.
Prize Postcard unique items:
There are three unique items (Gourmand's Ring, Lucky Ring, and Orichalcum+) that can be obtained from Prize Postcards, aside from the random assortment of items and materials normally received from them. Each of the three unique items can only be received once.
There are seven Orichalcum+ found throughout Kingdom Hearts 3. They are needed to craft/synthesize the Ultima Keyblade and are different than the regular Orichalcum. Successfully complete the indicated tasks to obtain all seven Orichalcum+:
Orichalcum+ 1: It is found in a chest on Exile Isle in The Caribbean.
Orichalcum+ 2: It is found in a chest in "The Final World". After completing "The Final World", go back to it to find a chest with the Orichalcum+.
Orichalcum+ 3: Collect 80 of the Lucky Emblems/Hidden Mickeys.
Orichalcum+ 4: Collect all 10 treasures in the Frozen Slider mini-game in Arendelle.
Orichalcum+ 5: Defeat the Eclipse Galaxy boss. To unlock this boss, defeat the enemies on each side of the cube, and it will appear on top of the cube.
Orichalcum+ 6: Beat the high score in all Flantastic 7 mini-games.
Orichalcum+ 7: Collect it from the Moogle shop Postcard Raffle; it is a random prize.
Bonus HP boosts
In "The Final World", after collecting 111 Sora copies, continue collecting copies instead of using the red portal. At 222 copies and 333 copies, you will unlock substantial, permanent HP boosts. After 333 copies, you will automatically unlock a cutscene.
To unlock the secret ending, collect a certain number of photograph Lucky Emblems scattered throughout the worlds. The amount required varies by the difficulty level. Collect 90 Lucky Emblems on the Beginner difficulty. Collect 60 Lucky Emblems on the Standard difficulty. Collect 30 Lucky Emblems on the Proud difficulty.
Schwarzgeist boss fight
First, get a Gummi ship with 200 speed. The easiest option is to get the Endymion ship from photographing the Endymion Constellation in Misty Stream Galaxy. The Schwarzgeist optional boss is found inside the large green tornado at the center of the Misty Stream Galaxy (second Galaxy you visit). Once the Endymion ship is unlocked, select it at the Embark screen to challenge the Schwarzgeist. You can also create your own custom ship with 200+ speed. Slower ships cannot fly into the tornado in the galaxy's center. During the boss fight, roll a lot to evade the attacks of the boss. Also, make sure to have the "Repair Kit" special weapon unlocked. It allows you to heal every 30-40 seconds. When your health gets low, just roll to avoid getting hit until your Repair Kit has recharged, then heal yourself. Keep repeating this method to defeat the Schwarzgeist and get the "Thermosphere" trophy.
Original music from Einhander
Enter the Schwarzgeist optional boss battle in Misty Stream Galaxy with the Endymion Gummi ship and its two Codymion small ships to hear the original "Thermosphere" music from the classic PlayStation game Einhander rather than the normal music.
Infinite Prize Postcards
Warp to the "Traverse Town: The Neighborhood" save point. Go to the Moogle Shop near the save point. Talk to the Moogle, buy a single potion, and exit the shop. You have a 50% chance of getting a Prize Postcard each time. Repeat this as many times as desired to get an unlimited number of Prize Postcards.
While on Monstropolis, do not use the Scream Strike when protecting Boo. The game will not progress until you use the Scream Strike, allowing you to keep getting more experience points. You can go from around Level 19 to Level 25 in approximately 15 minutes. Note: As your level increases, the amount of XP you get gradually becomes inefficient enough that it not worth continuing to use this trick.
Easy "Datascraper" trophy
The Flash Tracer courses are both found in San Fransokyo. The first is in the South District on a large bridge, and the second is in the North District on a skyscraper that has blue neon lights around it at night. You talk to the NPCs in these spots to start the courses.
Flash Tracer Course 1 (South District - 60,000 points for an "A" rank): This is the easier course. Finish it as quickly as possible to get a time bonus of 25,000 or greater, and collect all the rings directly on your path. Ignore optional rings that you do not necessarily have to fly or fall through (for example, the ones around the three poles at the very start are optional and should be skipped in favor of time).
Flash Tracer Course 2 (North District - 75,000 points for an "A" rank): This course is also heavily geared towards time. Equip a keyblade with high magic stats, as well as accessories that improve your magic stat. Kill all enemies using Thundaga (assign it to a button for quick use under the "Customize" menu). Also, equip Hi-Ether (or normal Ether) to refill magic. The enemies should die instantly from one use of Thundaga. If you have trouble, level up some more by replaying battle gates after the story. Additionally, equip the high-jump ability ("Ability" menu) so you can get the rings high in the air during the rail slide. On the last rooftop where lots of enemies spawn, use the carousel attraction to quickly defeat them.
Easy "Festive Dancer" trophy
You can only play the Festival Dance mini-game after completing the Kingdom Of Corona world. You can then fast travel back to this world and go to "The Kingdom Thoroughfare" fast travel point. Go to the market square where you danced during the story, and talk to Rapunzel. She will let you replay the dance, except this time you can earn a high score. During the story dance, you could not earn any points. A good strategy is to dance with the townsfolk by pressing X when they have a blue circle or Circle when they have a red circle. Then, press Square on the three pink circles that appear. Go to the next person, dance with them, go through the three pink circles, and repeat. If done correctly, pressing Square on the three pink circles will give +3 seconds. Only press the buttons when you are in the middle of the circle so you do three button presses total (one per circle). If you just mash the buttons, it may not give you bonus time. So try not to miss any pink circles and only do one button press per circle. When you take a dancing partner, let go of the Left Analog-stick for just a moment. It will automatically put you on the path to the next three pink circles. If you hold the Left Analog-stick, you can potentially press in the opposite direction of where the pink circles appear. The game puts you on the path automatically, but you still need to readjust a little bit with the Left Analog-stick after the circles have appeared. Do not press Triangle on the barrels, as they cost too much time. The goal is to maximize your chain by dancing with as many people as possible and get as many time bonuses as possible. With a 80+ chain, you will get 70,000+ points at the end and the "Festive Dancer" trophy. Dance until there is only one second left on the timer. Then, press Triangle to make everyone come together for one final dance. Even though time has run out, it will allow you to keep doing this special dance and increase your chain multiplier so you get an additional 15,000+ points. Simply press X on the blue and Circle on the red circles. Press the buttons when you are in the middle of the circle, otherwise it sometimes does not count properly if you press too early or too late.
Easy "Shield Shredder" trophy
You can only play the Frozen Slider mini-game after completing the Arendelle world. You can then fast travel back to this world and go to the "Mountain Ridge" fast travel point. Talk to your friends in front of the ice castle to play the Frozen Slider mini-game. A good strategy is to slide down the mountain without any crashes, and collect as many crystals as possible. To get a high score, do not lose your multiplier. You build up the multiplier by collecting crystals and not crashing. If you crash, you lose the multiplier. If that happens, pause the game and retry, as there is almost no way to beat the highscore. If you do the slide without crashing, you should easily get 600,000 points and the "Shield Shredder" trophy. Additionally, try always taking the left paths and sticking to the ground instead of using the air rails.
Successfully complete one of the following tasks to get a trophy:
KINGDOM HEARTS III Complete Master (Platinum): Unlock all other trophies.
Another Chapter Closed (Gold): Finish the game and view the ending.
Classically Trained (Silver): Get a new high score in every Classic Kingdom game.
Dreadnought (Silver): Fully power up the Leviathan.
Hidden Kings (Silver): Complete the Lucky Emblems section of the Gummiphone.
Leveled Out (Silver): Raise Sora to LV 99.
Master Chef (Silver): Earn an "Excellent" while preparing every type of cuisine.
No Stone Unturned (Silver): Complete the Treasures section of the Gummiphone.
Synthesist (Silver): Complete the Synthesis section of the Gummiphone.
Ultima Weapon (Silver): Synthesize the Ultima Weapon.
A New Journey (Bronze): Begin your brand new adventure.
A Wish at Twilight (Bronze): Adventure through Twilight Town and complete the story.
An Act of True Love (Bronze): Adventure through Arendelle and complete the story.
Bishop (Bronze): Defeat 3,000 enemies.
Blademaster (Bronze): Obtain a Keyblade that is fully powered up.
Centurion (Bronze): Score at least 12,000,000 pts. in Verum Rex: Beat of Lead.
Clash of the Gods (Bronze): Adventure through Olympus and complete the story.
Cornucopia (Bronze): Collect every type of ingredient.
Datascraper (Bronze): Get an A rank on both Flash Tracer courses.
Festive Dancer (Bronze): Score at least 70,000 pts. in the Festival Dance.
Full Course (Bronze): Earn your first "Excellent" while preparing cuisine.
Grand Mage (Bronze): Cast grand magic for the first time.
Happily Ever After (Bronze): Adventure through the Kingdom of Corona and complete the story.
Heartbound (Bronze): Use a link to defeat enemies for the first time.
Home Again (Bronze): Adventure through the Hundred Acre Wood and complete the story.
Inseparable Friends (Bronze): Adventure through Toy Box and complete the story.
Knight (Bronze): Defeat 1,000 enemies.
Know Thine Enemy (Bronze): Complete the Adversaries section of the Gummiphone.
Lasting Memories (Bronze): Hold on to 50 photos.
Making a Difference (Bronze): Adventure through San Fransokyo and complete the story.
Muscle Memory (Bronze): Get a new high score in one of the Classic Kingdom games.
One for the Books (Bronze): Complete the Game Records section of the Gummiphone.
Rook (Bronze): Defeat 5,000 enemies.
Salvager (Bronze): Use the gummi ship to obtain 20 unique treasures.
Say Cheese! (Bronze): Snap your first photo.
Shield Shredder (Bronze): Score at least 600,000 pts. in Frozen Slider.
Stargazer (Bronze): Use the gummi ship to find and photograph all the constellations.
Tall Enough to Ride (Bronze): Use an attraction to defeat enemies for the first time.
The Power of Laughter (Bronze): Adventure through Monstropolis and complete the story.
True Captain (Bronze): Sink 200 enemy ships in The Caribbean.
Way of the Pirate (Bronze): Adventure through The Caribbean and complete the story.
Additionally, there are five secret trophies:
Thermosphere (Gold): Destroy the Schwarzgeist, menace of the Ocean Between.
Flanmeister (Silver): Complete all of the Flantastic Seven missions.
The Battle to End All (Silver): Begin the final confrontation with Master Xehanort.
No Matter What (Bronze): Reunite with Kairi.
The Hearts Joined to His (Bronze): Gather the seven guardians of light.