Earthshaker

Unreleased Enigma is a Keyblade used by Terra during his quest to find Master Xehanort.

Terra is shown summoning his Keyblade differently than how most wielders do; his appears surrounded by translucent blocks in a flash of light, similar to how Roxas summons the Kingdom Key in the Simulated Twilight Town.

Like Ven and Aqua's Keyblades, it lacks a keychain. Because it lacks a chain, it is rumored to be a "false" Keyblade, however, this may only be speculation.

Kingdom Hearts II: Final Mix+
Terra uses this Keyblade to fight Sora after they save Disney Castle from the plunging darkness and so gives access to a wormhole in Kingdom Hearts II: Final Mix+.

During battle, Terra can change the Keyblade into a whip, a jet-ski like object, a fast spinning cog-like weapon, and a massive cannon, among other formations. It is unknown if Terra will have this ability in Birth By Sleep or if it only appears in his boss battle with Sora.