The unquestionably cute Victini is the first Legendary Pokemon you can catch in the game, at Level 15 no less. (Although technically it's a "Mythical Pokemon" because it's so rare.)
However you’ll need a ‘Liberty Pass’ to get hold of it. The Liberty Pass is handed out over Wi-Fi for a limited time, so make sure you get hold of one before you miss your chance, else there will forever be a hole in your Pokédex.
Once you have the ticket in hand simply head to the boat on the left most port in Castelia to ride to Liberty Island, here you’ll meet plenty of Plasma grunts. Once through these you’ll be able to catch the pesky Victini.
These two legendary monsters are exclusive to Pokémon Black & White respectively and caught through the process of the story or, in failing that, at the Dragonspiral Tower. Obtaining both will require a buddy to swap with.
Once you have the ability to surf head to the north of Route 6 and follow the water east to find the cave. You’ll need Flash if you want to see where you’re going, and more importantly you’ll need HM04 Strength to push the huge boulders--you can find it in the fourth gym’s city in one of the left most houses.
Simply navigate the cave and before too long you’ll find Cobalion standing in a dead end waiting for your challenge.
This aggressive looking beast is made available after you capture Cobalion. With the previous creature safely stuffed into a Poké Ball, a cave will open up toward the end of Victory Road.
From the road’s peak take the door on the right, take the stairs left, then push the boulder and head left to the cave entrance where the Pokémon is standing.
As with Terrakion, this gallant creature only appears after you’ve captured Cobalion. In this instance a new area will open up to the east side of Pinwheel Forest, simply head as far east as possible and then follow the tree line north. Head in and find the green stag just standing in a glade.
Found exclusively in Pokémon Black and White respectively, these two wind gods roam the land, changing location throughout the day, and they will run from battle very quickly.
After meeting your respective ‘mon during the story they will start to appear in the southern routes in the morning and then the northern routes in the evening.
The best way to capture these slippery foes is either with the Master Ball you receive during the story, or by utilizing moves such as Mean Look or Spider Web to disable the creature’s ability to flee from battle.
To find Landorus you need both Tornadus and Thundurus in your party, trade with a version of the other game to manage this, and then visit the Abundant Shrine by surfing to the left on Route 14.
With Tornadus and Thundurus in your party the all-powerful Landorus will glide down to attack you, be warned however that he is a Level 70 foe and not to be taken lightly.
Once you beat the story head to Route 13 and investigate the ‘Giant Chasm’, a location only available once you’ve seen the credits. Investigate the area by looping around the left and heading toward the middle in a spiral.
Before long you’ll reach the middle and the area will be frozen, head to the very north to find a cave in which Kyurem resides. Kyurem is Level 75 when you encounter him so make sure your team is up to the task before you attempt a capture.