The only way to be the best is to catch them all! So do just that! Or you can be a little hard-headed and go for the legendary Pokemon! Now i will only help you with Pokemon Black Version 2 and show you the Regi-trio, As that is the one most legendary are in! Here we go!

The legendary Regis'!: First, go to the back of clay tunnel and go through a door into a empty room with somebody there, and go to the middle of the eye in the floor next to a giant door, walk 9 steps down and 4 steps right, then press A. Now go into the giant door and you'll see a bunch of rock. Make your way through and go to the back. There is Regirock!!! Now catch him, and you will get a Iron key, after all of that save and restart the game and go to the main menu. Ok so, see the Unova Link button anywhere? Tap or select it and go to the Keys. Then go to the mystery door and tap the Iron key. (Btw the only way to get the Iceberg key is by trading it with Pokemon White Version 2 with the receive or exchange keys button) Now go back into the game, the chamber will be different! And Registeel will be there! Catch it! Thats all you need to know, now go to youtube and look it up, i suggest searching Marriland. And look for the (I think) Episode 87 of Marriland's Pokemon White 2 Version Adventure! And he will show you how to get Regiice, and Regigigas! Well good luck! And i got Regiice through Nintendo WFC trade!