This movie seems to be the best out of the trillogy. It isn't about the 3 Legendary birds anymore, but the legendary 'dogs'. The only thing we really dont' know is that how all the new characters fit in. Because we don't know the nature of the characters we cannot state thier role in the movie. We have translated the synopsis the best we could. This is offical and confirmed. It might be a little choppy:

As a young girl, Mi’s parents both passed away and she was left with the large inheritance, the Green Resort where one goes to gain peace of mind. The large property (Green Field) came with the Tower.

The strange Pokemon Annon (Gold/Silver) comes to Mi because of a strange card left by her father. Slowly Mi begins to lose sight of what is real and what isn’t. It seems that with the help of Annon, a crystal begins to enwrap the tower, blurring the outside world and making it all the more unreal for Mi. Annon creates the crystal tower for Mi to help her forget her solitunde and lonliness due to the death of her parents. Everytime she wishes for something, a piece of the tower becomes crystal. Gradually, her heart became crystal and then covered the entire tower.

Eventually it starts to enrap everything. Ash gets wrapped up into all of this because his mother, Haneko, is taken to the illusory tower because Mi wished for a mother, and Ash's mom, being a mother, was taken to the crystal tower by Entei, who appears as Mii's father in the Crystal world. Now Satoshi (ASH) must somehow rescue his mother and Mi from the powers of the tower. However they don’t want to leave because they believe they’re happy in the tower do to the powers of distortion it has and they no longer have a concept of the real world.

* It’s one of those trippy mainstream anime plots if you ask me. Think of Serial Experiments Lain.

And the added short movie—which is not Pikachu’s Birthday Party (as it was rumored), it's called Pichu and Pikachu---takes place in a big city which is a whole new world for pikachu. And I here there's music in this one. Singing pokemon perhaps? This movie also introduces an all new Pokemon, the baby Pikachu; Pichu!