Mario will be playable in an upcoming Kingdom Hearts game. The actual game described varies.
This is often part of April Fool's jokes.
If you beat Chernabog, then complete the time limit on Hades' Cup and complete every single battle on "Select Encounter" 10 times in a row, then you will be able to try Sora's Cup, where you build your own enemies that will compete.
If you beat Riku 1000 times on Destiny Island he becomes a playable character.
If you collect every chest in the game and go to the Waterway in Traverse Town, you will recieve Riku's Keyblade and Mickey's Keyblade.
If you make Wakka's ball fly into the water in Destiny Islands 15 times, you will see the cutscene from Final Fantasy X where Tidus jumps into the air and kicks the ball back to Wakka. Wakka gets automaticaly defeated and Goofy gets a weapon that is a Blitzball when you get him and Donald.
If you get all spells, complete the Hundred Acre Wood, then beat Ansem three times with the Ultima Weapon, you would get a Heartless Blade that was just as strong as the Ultima Weapon.
Completing the game without dying once and with only the Kingdom Key will unlock a secret ending cutscene.
Lies about Kingdom Hearts II[]
If you complete the whole game within 1 hour, you'll get the ability to play as Roxas through the whole game.
It is possible to meet Behemoths and Wyverns like in the trailer at the 1000 Heartless battle, if you manage to make Demyx summon water beings 75 times, and beat them all within 6.66 seconds (2/3 of 10), and get past the enemies after without getting the least hurt or for the other Final Fantasy guys to do a single point of damage.
Even though this is impossible, Behemoths and Wyverns were actually hidden in the code of the game. But they didn't have any animations and couldn't move at all.
If you kill Xemnas' Dragon within 30 seconds, you'll get to fight the last fight while on the nobody-ship like in the Dragon battle.
This too, is impossible because the cutscenes between each part of the dragon together, is longer than 30 seconds itself.
It is, however, possible to hack with a cheating device to use the nobody-ship in the last battle.
If you have a Save File from Kingdom Hearts Final Mix, where you defeated "Mysterious Man" on the same Memory Card as your Kingdom Hearts II Save File, you will fight Xemnas in the same room as in Final Mix, instead of the Skyscraper.
If you complete Jiminy's Journal and return to Disney Castle, a portal will appear in the Hall of the Cornerstone (in the original Kingdom Hearts II and not in Final Mix) where you have to help King Mickey fight a horde of Heartless inside it. After defeating the Heartless, King Mickey gives Sora the "King's Charm" which allows Sora to summon Mickey. An alternate version says that you must fight the Lingering Will to get it.