After Pitch Black and his Nightmare minions raided Tooth’s palace, Jack finds out that the baby teeth the tooth fairies keep contain memories of a person’s childhood. As Jack was suffering from amnesia, he wanted to get his baby teeth back in the hopes of unlocking the memories of his past. He then decided to help the Guardians in their efforts to avert Pitch’s plans to destroy the children’s faith in them, even though no child had ever believed in Jack in the first place.
Shredinger-Cat makes a beautiful Jack Frost! I’m just wondering if that’s real snow she’s crouching on? That would have been really cold for her in this light clothing! Thanks to Henry for suggesting this!
Source: Shredinger-Cat on Deviant Art