Shadow Form

Shadow Form is one of Sora's forms from Kingdom Hearts.

Temporary Form
Sora turned into a Shadow Heartless after his second fight with Riku. He is only in this form briefly and can only jump. However, due to Kairi's heart, he is able to recover into his human form again.

Side Effects
Since he was a Heartless, albeit temporarily, he created a Nobody that became known as Roxas. Oddly, Sora could not do a lunge attack like all other Shadows.

While this event gave birth to Roxas, it also gave birth to the unusual Nobody, Naminé, who is born from Sora's body and soul, but from Kairi's heart.

It is believed that this event triggered the side effect of creating the AntiForm when Sora was given his new clothes and Drive Form abilities a year later.