The Sandman and the War of Dreams - William Joyce

When the Man in the Moon brought together the Guardians, he warned them that they would face some terrible evils as they strove to protect the children of earth. But nothing could have prepared them for this: Pitch has taken Katherine. And now the Guardians are not only down one member, but a little girl is missing.
Fortunately, MiM has just the man to join the team. Sanderson ManSnoozy-known in most circles as the Sandman-may be sleepy, but he's also brave and strong and skilled at utilizing sand in a myriad of ways. If the rest of the Guardians can just convince Sandy that good can triumph evil, that good dreams can banish nightmares, they'll have themselves quite a squad. But if they can't they might never see Katherine again.