Gummi Blocks are essentially portable blocks of elastic material that have properties attached to them. They can be utilized in one form to create Gummi Ships, which are necessary to travel from world to world. Blocks can be found in chests, dropped from fallen enemies and ships and even purchased when Pinocchio and Gepetto are in Traverse Town. They can also be bought from Cid who eventually proves to be an expert in Gummi engineering and helps when Sora finds half of a Navi-G block in Deep Jungle.
A basic understanding of what Gummi blocks are can be inferred from the Ansem Reports. It appears that when Heartless appear, or when the door leading to a world's heart is opened, the wall that protects that world collapses. Gummi blocks then appear in said world, as in the case of Ansem's study of the meteors, suggesting that the blocks are remnants of the protective wall of the world. This would account for them appearing in many shapes and forms and bonding easily with each other. It is possible that Gummi is also present in between worlds, which might explain the presence of so many Heartless Gummi ships. The nature and origin of Gummi blocks allows them to travel to other worlds.
As mentioned in the Ansem Reports, Gummi blocks are "elastic" and "bond easily" when combined, as evident when creating Gummi Ships. The blocks themselves are very numerous and come in all shapes and sizes with properties attached to each. When added to Gummi ships, they provide advantages such as improved armor, increased acceleration and greater firepower. In both versions of Kingdom Hearts, specialized Gummi blocks can be used for other advantages, such as warp travel in Kingdom Hearts.
In the Original Kingdom Hearts, gummi travel was simple. the ship would move foward on it's own, and you could control up, down, left and right. The ability to brake was also included, but merely slowed the ship instead of a full stop. Numerous enemy ships would appear, and upon their destruction would leave a Gummi block or a blueprint for that enemy ship. The meters included in flight would consist of armor( substituting HP) and Power(substituting Mp). Certain blocks added additional meters, such as shield(From the Shield and Shield-2 blocks) and turbo(from the Haste and Haste-2 blocks) On the garage menu, you could create your own ship, with a block limit almost impossible to reach. Blocks could also be turned and colored for use.
While Gummi travel did not appear in Kingdom hearts: COM, it appeared in a different form in Kingdom Hearts 2. Although the System was more complicated, the concept became that of a mini-game. A path would have to be traversed once to get to a world, and then that world would become availible without the use of Gummi travel. However, each track has 3 missions with set goals and a score system, which acted as a side game that did not affect the story. Blocks would be awarded as prizes for score, and rarely dropped by a ship, which also included Nobody ships.The most notable features are the ability to urn the ship around during flight, the Overdrive feature, the concept of in-flight bosses, and the addition of Teeny ships, smaller ships that can fly along side you.While the game allowed for the customization of ships, completed blueprints were awarded for flight, based off of the Highwind, Invincible, and the Falcon, all airships of the Final Fantasy series. Bonus ships included the Tonberry, Moogle, Chocobo, Cactuar, Cat Saith and Fenrir, all modeled and named after characters or enemies in the Final Fantasy series.
Also, ship customization was improved as well. Along with coloring blocks, the player also has the choice of using block skins, which have special designs. New blocks were included, such as blades, shields, saws, propellers, and even wheels. Also, each block has a cost, instead of a "Block Limit". The most abstract feature is the ability system, which grants certain powers to the ship during flight