You will need Surf, Rock smash, and Rock climb. I suggest you keep a master ball for Dialga (you can clone it using the GBA Pokemon clone trick).

Go to Mt. Coronet, left from Hearthome city. Follow a path until you find a way out of the cave. But don't go threw it, go up and you will find a place where you can use Surf, go past it and go on land. Use rock climb on the wall, go up the stairs and follow the path to a door that leads to more stairs. Go until find a door that leads outside and move forward until you see a place where you can use rock climb just once.

Go left through the grass and go in the cave. Follow the path and you will be at spear pillar. Don't go up by the three people because they are the Team Galactics' generals. Save your game. When you beat them you will have a chance to catch Dialga.

Submitted by Mitchell Jorgensen