コロコロ

This month's issue of CoroCoro states that next month's issue will reveal a brand new Pokémon that is to appear in the ninth Pokémon movie, Pokémon Ranger and the Prince of the Sea.

Also of interest, is the narrator's remark in the teaser trailer: "Far, far away, somewhere in this sea, a legendary Pokémon that no-one has seen before is sleeping..." CoroCoro has hinted that the movie's formal title will also be announced as part of next month's coverage..
We'll have more info as it becomes available. 31 Days!