I Need Answers To Get On The Top Of Mt.Coronet On Pokemon Diamond?

Go to psypokes.com and look at the walkthrough or go to another site and see. All I can say is to keep looking around untill you find the cave to go through. You have to use rock climb to get to some of it. The fat guy will move after you beat the galactic grunts.

The only advice I can give you is to get the official guide for diamond and pearl from Game or Gamestation or Have a look online. I've completed most of the game just need to Catch em all lol.

i think you need suft or rockclimb

i got this-> FLY 2 OREBURGH CITY & heal bring your escape ropes, masterball & max repels,surf & rock climb pkmn along now from the pkmn center hop on your bike (fast gear) & go left & up then down the steps & up the sandy slope & right inside mt cronet surf across then go around & ROCK CLIMB UP & take the steps then go LEFT, LEFT & DOWN go up the steps & over the bridge then down & up the steps on your left side now go up & across the bride & down both sets of steps then acroos the way up the steps & out the doorway,continue you'll be at a 2 way go left,left & down & outside in the snow go right & up rock climb up & left take the steps through the grass until you find the doorway once inside go back & rock climb up & take out the grunt in your way continue and take out the next grunt continue on down the steps & outside in the snow again, take the steps & right face left & rock climb up take the steps & over the humps of steps then go around & right inside conitnue 2 take out the 2 grunts on your way continue until your outside on the very top of the SPEARL PILLARnow prepare 4 battle but not alone your rival's 2 join you 4 this double battle ,when done take out CYRUS when done go catch DIALGA but not yet prof rowan & his assistant will come talk 2 you about DIALGA now take 2 steps & SAVE now go catch DIALGA,glad 2 help :)