Earthshaker

Unreleased Terra's Keyblade is a Keyblade used by Terra in the upcoming prequel Kingdom Hearts Birth by Sleep.

Kingdom Hearts II Final Mix
During the battle with the Lingering Sentiment, the Keyblade can change into a whip, a jet-ski like object, a fast spinning cog-like weapon, and a massive cannon, among other formations, like making the Keyblade quadruple in size. It is unknown if Terra will have this ability in Kingdom Hearts Birth by Sleep, or if it only appears in the Lingering Sentiment's boss battle with Sora. However, on the Birth by Sleep official site, it shows Terra on a jet-ski with similar properties from his Keyblade in the World selection screen.

Kingdom Hearts Birth By Sleep
This particular Keyblade appears in the game as Terra's main and default weapon; it is unknown as of yet if he is able to currently equip other variations. Recent screenshots have shown a somewhat redesigned Keyblade with a keychain at the end of the hilt, which resembles a rock fragment. It is revealed that Terra can turn his Keyblade into a bike and ride it to other worlds like a Gummi Ship.

Trivia

 * It is interesting to note that the Keyblade that is used by the Lingering Sentiment and by Terra in the secret video "Birth by sleep" seems to be different that the Keyblade Terra uses during gameplay. Though both are of seemingly the same design, the former is much larger with slightly different teeth.  This Keyblade also lacks a keychain, while the one Terra uses in gameplay possesses a rock-like keychain.
 * The keychain on Terra's Keyblade appears as a conical rock fragment. This is notable as Terra means "Earth" in Latin.  The same can be said of Aqua's water-themed keychain (Aqua meaning "Water") and Ventus's wing-themed keychain (Ventus meaning "Wind").