AntiSora

The Anti-Sora was a shadow duplicate of Sora that Riku created to show his power of darkness to Sora. It appears in Kingdom Hearts, in the Neverland world. Additionally there are regular enemies in Neverland called "Shadow Sora", whom are merely darkened models of Sora without keyblades; they are very weak but have high HP, and their attacks make you lose massive amounts of munny. However, they in turn drop loads of munny and HP balls when defeated.

Kingdom Hearts
Sora meets up with Riku in Neverland, where Riku reveals he now has control over the Heartless. To prove this, he creates a Heartless version of Sora before Sora's eyes. Sora encounters these Shadow Soras several times throughout his adventure on Captain Hook's ship, although they have no weapons and often disappear before he can destroy them. Only Sora is able to damage these enemies, and none of his partners will attack them.

When Sora makes his way to the captain's quarters, Riku creates Anti-Sora, an exact clone of Sora with large, yellow eyes. Anti-Sora used the same keyblade attacks as Sora, but could also become a shadow like the namesake enemies.

When Sora defeats it, Anti-Sora falls back into darkness, droping the Raven's Claw on the way.

Trivia

 * Anti-Sora is one of only two characters who do not have entries in Jiminy's Journal (the other being Chernabog).
 * Anti-Sora strongly resembles the Anti Form from Kingdom Hearts II.