How to Catch Kyurem in Pokémon Black or White

Gain access to Lacunosa Town by completing the Pokémon League. Lucunosa town is located east of Opelucid City, at the end of Route 12.

Once in Lacunosa Town, make sure you are stocked up on Poke Balls and healing items as the battle will be quite a challenge (it is level 75 after all). Then take the exit on the right towards Undella Town via Route 13. (If you are coming from Undella Town, bypass Step 3). If you went this way, bypass Step 4.

When you get there you will be greeted by the confusing yet quite small Route 13. Once there, go south (battle the trainer if you wish to), go through the first patch of grass, preferably on the right hand side as you can collect an item (and avoid another patch of grass). Then hop over the ledge, and keep going until you reach the clearing. Then turn left and go down the steps, through the patch of tall grass and keep to the face of the cliff (to the hero's right). Make a left when you reach the end of the beach and walk up to the far-off set of steps. Climb them, and continue onwards to the Giant Chasm. Make sure you use HM Strength to move the boulder in case you lose to Kyurem so you can quickly access it again.

If you started this event from Undella Town, your journey is much simpler. You have to arrive at Route 13 (after stocking up of course), go up the steps and follow the beach, staying as far right as possible (but do NOT turn at the end of the second set of steps to go down the very narrow alleyway of sand as this will lead you back to the start of Route 13). Then you reach the steps and continue on (also making sure to move the boulder using HM Strength).

Once this is done, you will arrive at Giant Chasm. It looks very simple at first, but many challenges await you. First you must enter the cavern in the middle of the entrance. Once inside you will be in a dark room. You may collect items if you wish (as there are a couple of rare items in the whole of the chasm), but the main goal is to reach Kyurem. Firstly you need to go all the way around the cavern and reach the exit (HM Surf is required at this point so make sure you have a Pokémon who can use this!). Once you exit, you will return outside.

You will be introduced to an extremely large and complex maze for you to go through. The objective is to get to the middle where a pond-like area of water lies. This looks impossible at first, but there is a way. To do this, the easiest way (without wanting to collect items) is to go as far North as you can from the entrance, then as far West, then as far South, then as far East, then as far North again (make sure you do not go over a ledge which takes you to a part where you have already been, as this mucks up the order). Then go through a patch of long grass and you will see the pond like area. Go to it and you will hear an Earthquake-like roar.

After this sound, the ground will cover with snow (the roar was Kyurem and the snow was his doing in case you hadn't realized. This now gives you a clear passage to the exit and the final cavern in which Kyurem is inside. Walk through to the exit.

Once inside the cavern, getting to Kyurem is a doddle. Simply walk up to him and interact with him. As all legendaries do, it will roar, and the battle will begin.