To get to Mt. Coronet, you are going to need your HM slave with strength. Fly
to Hearthome city and head west, Route 208. Enter the cave and once inside, you
will need to go north. At the very top of Mt. Coronet is Dialga so be ready for
a legendary battle. Bring about 30 Ultra Balls,4 Quick Balls and 6 Timer balls.
Dialga will be lvl47 and is a steel/dragon type. If you are playing Pearl, you
will not get Dialga but instead will see Palkia. Palkia is a lvl47 water /
dragon type.
When you first enter the cave, you need to head west to the opposite side. Once
you reach the west entrance, head north and surf across the pond. Use rock
climb to reach the stairs up. You should seen Bronzong somewhere along the way.
It is the evolved form of Bronzor and is new to the pokedex. In the next room:
North, West, South, Upstairs, North, West over bridge, down stairs, up north
stairs,up stairs, cross bridge, down stairs, down stairs, upstairs and in cave
door.
Next room: Up stairs, up stairs
Next room: up stairs, trainer battle, west, south, trainer battle, Out.
Now you are outside. Follow the path and use rock climb when you get there. Now
instead of using rock climb again, head west and through the grass until you
reach another cave. Inside, use rock climb, follow the path, down the stairs
then east out of the cave.
Outside again. Through the grass, down the stairs, rock climb west. Down the
stairs, through the grass, keep going west and you find another cave. Enter.
There is only one way to go through here so keep following the path, eventually
you emerge at the very top. Inside the cave, there is also Chimecho.