Charizard Rider wrote:
Primal Dialga is in Explorers of Sky, to the best of my knowledge. I have Explorers of Darkness. So it'd be after I beat regular Dialga, right?
Primal Dialga is in Explorers of Time, Darkness AND Sky. So after going through the Hidden Land and Temporal Tower for the first time, you battle Primal Dialga (doesn't matter which PMD2 game). After you defeat Primal Dialga, the credits will roll. When the credits finish, more dungeons are available - including Steam Cave.
Oh, and defeating regular Dialga can only be done once Primal Dialga is defeated.