This Pokemon is said to appear every 1000 years for seven days and it is awaken when stars are shooting.

Jirachi, the star-shaped Pokémon,  is the main Pokémon in the 6th Pokémon movie. According to the Pokédex, Jirachi is a wish-Pokémon and it uses it's telepathy  to relay a tearful message.

Masato will be choosen by Jirachi to hear his voice and it's thoughts..

According to the Pokédex. Absol is a Pokémon that whenever appears is said to bring catastrophic consequences.

Absol, is the protector of Jirachi, and it will do whatever it's in its hands to help Jirachi.

This Groudon, will be resurrected by Butler. But it's not the real Groudon, it's just an something similar to an illusion. This Groudon will be able to produce tentacles

Butles is the magician of the Pokémon Theme Park that Ash and company visit. He was once member of the Team Magma and worked as a scientist.
His goal was to resurrect Groudon, but he failed to and was fired form Team Magma. Even that, he still tries to bring back Groudon to life and whatever cost.

He is also the owner of the coccon from where Jirachi will come out later on the movie...

Butler owns three Pokémon: Mightyena, Salamance and Kirlia