After beating the game you can earn something called Pokemon Radar from one of scientist working in prof. Syncamore Labs. This should be used in tall grass and it will do something that will help me find best/strongest pokemon with best stats.
But whenever I'm in tall grass and I wanna use it I heard my in-game Mother voice that it isn't good place.
Where can I use it? Or am I using it passively and I didn't know it?
Best Answer
No, you are not using it passively :p.
To use the Pokemon Radar:
Up to 4 patches of grass will shake. (It technically always chooses 4 spots around you but most patches of grass are smaller than it's range, so it may 'shake' a position that is not tall grass and therefore you will see less than 4.)
If you go into the shaking grass it is very likely that you will fight a pokemon. It is not guaranteed though.
After each battle four more spots will shake. If you choose a spot with the same pokemon as the last one you fought the cycle will continue. This is part of a chain.
Speculation: It looks like some spots will shake with more intensity than others. The less it shakes the less likely the pokemon in it will be the same as the one you just fought if there is any pokemon at all.
You will end the chain if:
Helpful Tips:
http://bulbapedia.bulbagarden.net/wiki/Pok%C3%A9_Radar