Just remove Arcuse. Darkrai, Giratin, dialga and palkia is fine. How about this: team galatic hunting Giratin because it has the power to go tn another Dimension. If they can catch Giratina they can go to the Time and space dimension and can catch Dialga and Polkia. But first they need to Catch Giratina but they can't go to Distrotion World known as Revers world. They found that Darkrai has the power to open a portal to distrotino world.
They many time try to catch Darkrai but failed. So they come up with a plane. They caught Mewtwo and control him by a device. Mew two open the Portal of Distrotion world.
Darkrai notic that something wrong but he have not enough power to stom them. So he tell the playe{my game hero} in a dream about what hapaning. And than.....You know.
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ok how is the story.