4th Gen Darkrai, Shaymin, and Arceus

[Deniance]

How do you get Darkrai, Shaymin, and Arceus?

 

[Forci Stikane]

Darkrai was released as a movie event. You can't get the other ones yet.

A simple forum search would have brought you to several threads asking that question...

 

[PokeRandom]

Through official pokemon events or by using cheats eg. Action Repley.