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, dropping the Raven's Claw on the way.

Kingdom Hearts II
Sometimes, when using Drive in battle, Sora turns into Anti-Sora and he runs on all fours. Anti-Sora is able to move as fast as Sora does in the Pride Lands as a lion, and uses fast combo attacks to attack the enemy. Unfortunately, Anti-Sora is not able to fight with a keyblade in Kingdom Hearts II. Even though this is so, he does provide a satisfactory exception if he switches to Anti-Sora in combat.

Trivia

 * Anti-Sora is one of only three characters who do not have entries in Jiminy's Journal (the other two being Chernabog and Glut).
 * Anti-Sora strongly resembles the Anti Form from Kingdom Hearts II, except for the fact that Anti-Sora's outfit is purely black, while Sora has greyish flames on his black pants while in Anti Form.
 * Anti-Sora is, in a way, mirrored by the Shadow Roxas that appears in Kingdom Hearts II.