You have to own the key. Look around in the Team Galactic Head Quarters, it is in there somewhere. After you find it, keep searching the Team Galactic HQ until you find the leader. Battle him. After you defeat him, go through the portal. Then battle the next person and save Uxie, Azelf, and Mesprit. You will then follow the remaining portals and escape. Then you must go to the Hearthrome City side of Mt. Coronet with Rock Smash, Rock Climb, and Strenght. BRING VERY STRONG POKEMON!!! DON'T MAKE THE MISTAKE THAT I DID BY BRINGING YOUR LEVEL NINE ONIX SO IT CAN USE ROCK SMASH!!! Hike all of the way to the top. Then deafeat the two commanders followed by the leader. AFter that, Professor Rowan tells you to battle Dialga. Here is a tip: save the game before trying to catch. If you lose it, turn the game off and then back on and try again. It normally is easy to catch. I caught it with one ultra ball when his energy was still green (he made my last high leveled Pokemon faint). I think that the more he is weakened, the less he likes you, and the less he wants to be caught.
After defeating Team Galactic, you can catch Dialga in the Spear Pillar.
You have to beat the team galactic leader, then dialga comes out.
it holds dialga still so team galactic could have dialga's power
you have to go to the spear pillar when team galactic is there
hes no where but you can see Saturn in the galactic hideout
you go and battle dialga
After you have the 7th badge, go into mt. coronet. Keep going up, and battle all the team galactic morons who wanna battle you. soon youll see a cave. go in and beat two team galactic commanders and the galactic boss. then dialga is waiting!!!
You have to have Dialga. Dialga is at the top of Mt. Cornonet, you must enter in from Hearthome Cuty, or Dialga will not be there. From Hearthome, you have to climb all the way to the top, and Dialga will be at the Spear Pillars with Team Galactic.
You Have To Go To Spear Pillar and catch it there but you have to battle the team galactic though then you can catch it. Have a nice time catching Dialga :)
If you have already caught Palkia or Dialga (Palkia-Pearl Dialga-Diamond) then that means that you have already defeated Team Galactic, and you can go to the Pal Park, try to find more legendaries, or anything you want to do, but if not then you have to go to the place where you will catch either Palkia or Dialga and right before you catch them you will encounter Cyrus, the leader of Team Galactic. If you want to know where to find Palkia or Dialga and encounter Cyrus try looking up something like "where do you catch Palkia or Dialga?" or something like that.
you have to go to hearthome and gain dialga or palkia
you could catch palkia and dialga