Summary
Mt. Coronet is the mountain which divides the western part of the Sinnoh region from the eastern part. At the peak of the mountain is the Spear Pillar, where Dialga and Palkia can be found (as well as Arceus, by using the Azure Flute. Apparently, people outside of the Sinnoh continent can see it. And because of its magnetic properties, Magneton and Nosepass evolve into Magnezone and Probopass, respectively.
Mt. Coronet
Game Plotlines
In Pokemon Diamond and Pearl, you follow Cyrus and Team Galactic here to stop them from creating a new world, in Platinum, you do the same thing but just as you are about to fight Cyrus, Giratina does the job for you and pulls Cyrus in to a parallel Dimension.
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