Mii is a small girl whose parents disappeared when she was little.  A bunch of Unown, sensing her pain, try to help her by creating an illusionary world.  With the help of Entei, she tries to create a surrogate family by stealing Hanako.  Mii is angry when Satoshi-tachi try to break her illusion, but she soon comes to the realization that living in a fantasy world is not healthy.

Professor Spencer Hale/Shurii

Shurii is Mii's father who was researching the Unown.  He disappeared when the Unown pulls him into another world.

Lisa/Rin

Rin meets Satoshi in his travels through the Jouto League, and decides to join him on his quest.  Like Satoshi, she too wants to become a pokemon master.  She shows Satoshi how to get to Green Ville, where the majority of the movie's main events occur. 

Unown/Unown

Unown is a mysterious floating pokemon.  It's black and has one eye, but other than that its shape can be one of 26 different varieties.  Yup, there are 26 different kinds of Unown, one for each letter of the Roman alphabet.  In the movie, the Unown gather to create an alternate reality for Mii, a reality in which she doesn't have to deal with the sadness of her father's death. 

Entei/Entei

Entei is one of the Legendary Dog (or Cat?) pokemon in Gold/Silver.  Entei, which is able to talk, is the one who kidnaps Hanako and acts as Mii's father.  It serves Mii, but is also known to help Satoshi-tachi.  What side is it on?