If you use the Poke Radar at the end of the game, you can get many Pokémon in Diamond/Pearl.It can help you find some common ones that you really, really want.When you're in the small grass, knowing how to use the Poke Radar can be useful.
Step 1: You have to complete the Sinnoh Pokedex.
You don't have to catch all of them.If you talk to Professor Oak in front of Pal Park, he'll give you the Poke Radar.
Step 2: Go into the grass field.
You'll have to find some because the Radar only works in short grass.If you use a repel, it will make it so that you only encounter the Pokémon found in the shaking grass.Make sure you don't ride your bike.You can use the radar to find the spot you want.
Step 3: The grass is shaking.
You have to keep a record of which patches were shaking.For more chance at finding the same Pokémon, aim for grass farther away.As this heightens the chance that the radar will not find any more shaking spots, be careful not to go to grass right on the edge.Recharging the radar is what you should do if this happens.
Step 4: If necessary, replenish the radar.
If the shaking grass patches are different from the ones you've seen before, this can be helpful.To do this, walk 50 steps and be careful not to run into a shaking patch or let your repel run out.
Step 5: You have a chance to defeat the Pokémon.
The grass around you will keep rustling if you defeat the Pokémon.This saves time because you don't have to keep up with the radar.
Step 6: persist, persist!
You'll meet dirt common Pokémon a lot.Don't worry.The Pokemon that you can catch with the Poke Radar are rare.There's a high chance you'll meet the Pokémon more often if you meet it once.
Step 7: The grass is sparkling.
There is a chance that there is an ultra rare shiny Pokémon if the grass is sparkling.