The title to DP113 has been revealed as The Mischievous Phione! It will air on February 5th in Japan. Phione is, of course, Manaphy’s baby when pairing the legendary with a Ditto.
With the appearance of Cresselia recently and Phione in a few weeks, the only Diamond and Pearl legendary Pokemon left to show are Heatran and Arceus. The three pixies may count as well, though the animé has already shown their silhouettes.