Yukinari (ユキナリ) / Sammy

Japanese VA:  Toda Keiko
English VA:  Tara Jayne

Yukinari was drawing one day when it noticed Celebi running from a hunter, so he decides to help it.  Later, Yukinari is brought forty years into the future by the pokemon.  As the young Pokemon Watcher works to protect the time-traveling pokemon, he befriends Satoshi and forms a close bond with the young trainer. 

Vicious (ビシャス) / Iron Masked Marauder

Japanese VA:  Shirou Sano
Pokemon in Hand:  Bangirasu, Hassamu, Nyula, Celebi (temporary)

Vicious is an elite member of the Rocket-Dan in search of Celebi, the super rare time traveling pokemon.  He has supposedly developed a "Dark Ball" that turns the pokemon he's captured with it into evil creatures.  Using his spider-like mecha named Gareosu and his Dark Balls, Vicious is a trainer who will use any means necessary to achieve his goals.

Towa (トワ) / Towa

Japanese VA:  Koyama Mami
English VA:  Veronica Taylor

Towa is the kindly woman from forty years ago who tells Yukinari about the "voice of the forest."  Forty years later, she is able to recognize Yukinari as the young boy who had vanished with Celebi all those years before. 

Miku (ミク) / ???

Japanese VA:  Suzuki An

Miku is Towa's granddaughter and 

Celebi (セレビィ) / Celebi

Japanese VA:  Sugiyama Kazuko
English VA:  Sugiyama Kazuko

Celebi, the "Myuu of Pokemon Gold/Silver/Crystal," is the star of the movie.  It is being hunted by Vicious because it is so rare and powerful.  Celebi has the ability to travel through time, and it uses this ability to bring Yukinari forty years into the future.

Suicune (スイクン) / Suicune

Japanese VA:  Tanaka Masahiro
English VA:  Tanaka Masahiro

Suikun is the guardian of the forest that Celebi's been hiding out in, and it gets angry when Vicious' mecha starts stomping around in its forest.

Kakuleon (カクレオン), Whaleko (ホエルコ), and Ruriri (ルリリ) / Kecleon, Wailmer, and Azurill

Japanese VA:  Takada Yasuhiro (Kakuleon), ??? (Whaleko), Kawada Taeko (Ruriri)

These three new pokemon made their video game debut in the Pokemon Ruby/Sapphire game.  Kakuleon is a chameleon that comes in different varieties, much like the Unown.  Whaleko is a whale pokemon that is often used to ferry trainers from one location to the next.  Ruriri is the pre-evolution of Marill.