A Giant Shadow
With the Keyblade in hand, Sora becomes more confused than ever before. A Darkside then appears before him, forcing Sora to flee. Suddenly, the voice from before appears, encouraging Sora to not be afraid. Sora decides to stand and fight, proclaiming his experience through sword fighting with Riku. After fighting the Shadows to seamlessly no end, Sora realizes he needs to take down "the big one". He then leaps into the air, striking the Darkside in the head, thus defeating it with a single blow.
(Numbers indicate order of appearance.)
Items of note
Kingdom Hearts references