white grass will get you a better Pokemon.
if you mean the map marker you can catch mesprit Pokemon of emotions with it hope this helps
above jubilife city in the grass by using Pokemon Radar
no its only avalible on a pokemon event
did you mean sunkern if so you can catch him/her using a poke radar on route 204
At the summit of Mt. Coronet using the poke radar.
You can't catch a Taillow in Pokemon Platinum, but you could catch the later evolution (Swellow) using Poke Radar on Route 213, and then breed it to get a Taillow.
You can find Smeargle in route 212 using the Poke Radar.
you catch them in all of the lake surroundings using your poke-radar which you get after you beat the elite four hope i helped :)
i know you can catch a ditto
Go to the Trophy Garden which is in the Pokemon Mansion. porygon is rare in Pokemon Diamond, so using the Poke Radar would be easier.
You can find it in the northern portion of Route 210 but only when you're using the Poke Radar.
If you use the Poke Radar you will have a chance of getting a shiny Pokemon. But the actual Pokemon will not USUALLY change by using the Poke Radar.