How do you get Dialga in Pokemon Platinum?

Answer 1

You have to get the adamant orb then go back to spear pillar there is a blue opening click on it and you battle diagla
If you go up to Spear Pillar again, but take a Pokémon that knows Waterfall with you. On your way up the mountain, there is a waterfall (inside) that has a cave above it. Go up the waterfall and into the cave, where you will find the Lustrous/Adamant Orb. Then head up to Spear Pillar where you will find what you're looking for.
After getting the National Dex, go to the room above the waterfall in mt. cornet, in there is the lustrous and adamant orb. You also need to talk to Cynthia's Grandmother in Celestic Town but with the 2 orbs, you then head to Spear Pillar where Giratina was and there should be a blue or pink portal, if the pink appears first, battle Palkia then leave and enter again and the blue portal will be there.

They're both level 70.

only an ignorant person would say that first go talk to to cynthia's grandma after that you HAVE to get those two orbs before battling the elite four get them go to the spear pillar and the color portal that shows up first will depend on whether you pick the blue orb first or the pink one blue being dialga pink being palkia.PPPPPPPPPPPPPWWWWWWWWWWWWWNNNNNNNNNNEEEEEEEEEEEDDDDDDDDDDD