go to the top (of the inside, so use the stairs) of the mountain below the safari zone.
Duskull is uncommon, not rare but its better to catch it if you don't have one
on the moon
Pokeradar on Route 224. It's easier just to catch Duskull in the Lost Tower at Night in Platinum. (Duskull don't appear there in D/P, only Platinum.)
You can catch Duskull in Pokemon Platinum by going to the Lost Tower that is near Solaceon Town however you can only find it at night.
It is very rare but you can catch it at mount Pyre.
Use PokeRadar on Route 224. There is a 2% chance and the Duskull will be level 23.
Turnback cave.
On route 224 with the pokéradar.
After you catch giritina youll come to spring field and it will be there in the grass!
Route 224 Poke Radar
you have to catch a duskull on route 224 and raise him to get dusclops
you evolve it from duskull or catch it in tower with the two orbs