Kyurem

"Do you think you're worthy of battling me?"

Kyurem is a legendary Dragon/Ice type pokemon introduced in Pokemon Black 2 and ''Pokemon White 2. He is also the primary antagonist of the fifteenth Pokemon movie, Kyurem vs. the Sword of Justice.''

Black/White 2
The final boss of the games, Ghetsis controls Kyurem near the end of the main adventure and makes it do battle with the player, but not before ordering it to either kill or simply freeze the player. After the player defeats Ghetsis, the Elite Four, and captures or beats either Zekrom or Reshiram, the player can go back to where Kyurem resides and either make it faint or capture it. If the player chose to ccapture Zekrom or Reshiram, they can be fused with Kyurem, using the DNA Splicers, to form either Black Kyurem or White Kyurem.

Kyurem vs. the Sword of Justice
In the movie, Kyurem lives in an abandonded mining complex in a mountain. He apparently lives in quiet solitude and rarely interacts with the outside world. His solitude is interrupted when another poemon, Keldeo, chalanges him to a battle in his mine. Kyurem seems to be uninterested in the fight, asking Keldeo if he believe he is worthy enough to fight a creature as powerful as Kyurem. Keldeo manages to get the Dragon's attention when he claims that he is a Sword of Justice, which is actually a lie. Kyurem accepts Keldeo's challange. Since Keldeo lied about being a Sword of Justice, he wasn't ready or strong enough to fight Kyurem. Unsurprisingly, Kyurem easily overpowers Keldeo, and even manages to break his horn off in the process. Keldeo succumbed to his fear of the Dragon and fled. This angered Kyurem, and made him relentlesly pursue Keldeo.