Kyurem

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

- Kyurem questioning Keldeo's challenge.

Kyurem is a legendary dual-type Dragon/Ice Pokemon introduced in Pokemon Black and ''Pokemon White. It eventually played a pivotal role in their sequels, Pokemon Black 2 and Pokemon White 2''. In most of its appearances, it is portrayed as a villain. 

The Legend of Kyurem
Kyurem is an extraterrestrial Pokémon. However, one resides in the Giant Chasm in the Unova region after it apparently fell from a meteor. An old legend in Lacunosa Town describing Kyurem claims that it would take people and Pokémon away from the town and eat them. It is unknown how much credence there is to this story, however.

Black/White 2
The antagonists of the games, Team Plasma, controls Kyurem from their aerodynamic base, using its power to freeze Opelucid City. Ghetsis, and several Grunts claim that they intend to freeze all of Unova with Kyurem's power. Near the end of the main adventure, Ghetsis takes personal control over Kyurem 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 Reshiram or Zekrom, the player can go back to where Kyurem resides and either make it faint or capture it. If the player chose to capture Reshiram or Zekrom, they can be fused with Kyurem, using the DNA Splicers, to form either White Kyurem or Black Kyurem.

Kyurem VS. The Sword of Justice
In the movie, Kyurem lives in Full Court, an abandoned mining complex inside a mountain. It lives in seclusion and rarely interacts with the outside world. Kyurem is considered the strongest Dragon-type Pokémon in the world, having been born at the same time as Reshiram and Zekrom. It can harness the powers of both Reshiram and Zekrom at will, allowing it to transform into White Kyurem and Black Kyurem.

Kyurem's solitude is interrupted when another Pokemon, Keldeo, challenges the Boundary Pokemon to a battle in the mine. At first, Kyurem seems to be uninterested in the fight, asking Keldeo if he believed he is worthy enough to fight a creature as powerful as Kyurem. Keldeo manages to get the Dragon's attention when he claims to be a Sword of Justice, which is actually a lie. Kyurem accepts Keldeo's challenge, and creats an arena on a platform outlined by icy pillars. Since Keldeo lied about being a Sword of Justice, he is not ready or strong enough to fight Kyurem. Unsurprisingly, Kyurem easily overpowers Keldeo, and even manages to break his horn off in the process.

During their battle, the real Swords of Justice (Cobalion, Terrakion and Virizion) enter Full Court and attempt to call off the fight before Kyurem eradicates Keldeo, only for the Dragon to freeze them solid to prevent them from interfering with the battle further. Keldeo succumbs to his fear of Kyurem and flees. This angers Kyurem, who then relentlessly pursues Keldeo in order to finish their battle. Its search leads it to find an almost unconscious Keldeo on a train, where Ash, Iris, and Cilan were attempting to help Keldeo. Kyurem is forced to jump off the train when it enters a tunnel.

Eventually, Kyurem arrives in Roshan City with a small army of Cryogonal (his 'friends' according to Cilan) where it changes into White Kyurem and continues pursuing Keldeo. After finding the group and getting attacked by Pikachu, Kyurem again changes, this time into Black Kyurem, and flies up to a signal tower while his Cryogonal continue the chase. Keldeo's newfound friends try to lead Kyurem away from him so he can save the Swords of Justice back at Full Court. In the first attempt, Iris leads Kyurem to believe that Keldeo is in a blimp, but when Kyurem sees it is only Iris and her Axew, the Dragon angrily freezes the propellers, making the dirigible fall. Next, it brings an old train engine to a stop with ice, thinking it contains Keldeo, but after discovering only Cilan and his Pokemon within, it flies off and transforms back into White Kyurem, returning to Full Court.

Kyurem arrives back in Full Court minutes before its foe and remakes the arena from earlier. Kyurem then notices Ash and his Pokemon attempting to free the Swords of Justice. Kyurem is angered, not because of what they are doing, but because a human had entered its home and realm. It attempts to atack them, but Keldeo deflects its attack. Keldeo then admits to Kyurem that he lied about being a Sword of Justice, but the Boundary Pokemon reveals it knew that Keldeo was lying from the start. Kyurem then demands that they end their battle.

After gathering the courage to face Kyurem again, Keldeo shifts into his Resolute Form and continues his battle with Kyurem. As in the first round, Kyurem initially overpowers Keldeo with ease. Eventually Keldeo's horn regrows as he shifts into his Resolute Form, ending up longer than before and glowing, similar to that of a real Sword of Justice. This makes the battle more even-sided for a while, but Kyurem again gains the upperhand by freezing Keldeo solid, seemingly ending the fight. However, Keldeo's newfound power and confidence allow him to break free, earning him the move Secret Sword. With it, he lands a direct hit on Kyurem, who becomes pleased by the turns of events and witnessing Keldeo's true strength which made him a match for the Dragon's power. Kyurem then attacks at full strength by unleashing another attack, which Keldeo also deflects, but the attack heads straight for Ash, his friends, and the now freed Swords of Justice. Rather than let them be hurt, Keldeo jumps right in front of the attack, taking the brunt. This causes him to fall back into the arena and come dangerously close to losing consciousness again. Kyurem then pins him to the ground by placing his foot on Keldeo's regrown horn, and Keldeo admits defeat.

Rather than finishing the battle, Kyurem removes its foot from Keldeo's horn and transforms back into its normal form. The Dragon verbalizes its surprise that Keldeo chose to protect his friends rather than pursue victory, therefore earning Kyurem's respect. Kyurem then tells Keldeo that the Colt Pokemon has "a fine Sword" before lumbering off to return to its solitude. The entire mining complex soon begins shaking and collapsing due to the battle from earlier. Keldeo and all its companions make a break for the outside, but Kyurem simply looks up at its crumbling home and changed into White Kyurem to simply freeze the collapsing pieces into place, coating them in a thick blanket of ice. Ash and company let out impressed statements about Kyurem's "castle of ice" as it lumbers off back into its home.

Pokemon Mystery Dungeon: Gates To Infinity
Kyurem makes an appearance as the secondary antagonist in the 3DS game, Pokémon Mystery Dungeon: Gates to Infinity, and is referred to as male.

He resides in a massive structure composed entirely of ice known as the Glacier Palace, the existence of which was unknown prior to the events of Gates to Infinity. When the two protagonists and their companions travel to the mysterious Great Glacier in search of a fabled crystal that enable levitation, they enter the Glacier Palace and discover a corridor in which no one but the player is able to breathe. After all of the companions collapse, the room becomes dark, and Kyurem descends into the hall from a cloud of mist that hides the ceiling from view. He informs the player that he had foreseen their arrival, but the path before them cannot be trodden. The legendary Pokémon commands the travellers to leave and rewards them handsomely for their efforts.

The player encounters Kyurem again after he/she and his/her partner escape from Munna's thugs through the Scorching Desert. Hydreigon, the duo's current companion notes that deserts are naturally cold at night, so the sudden arrival of the ice dragon takes all three of the Pokémon by surprise. Without mercy, Kyurem proceeds to freeze Hydreigon solid and crush the resulting block of ice, thus destroying Hydreigon completely. With the lesser dragon out of the way, Kyurem then charges at the player and brutally stomps him/her into the dust, relenting only when the partner begs him to stop. Seeing that the partner Pokémon has lost the will to resist the future of destruction that the Bittercold (formerly known as the Great Crystal) ensures, he decides to have mercy on the player, believing that without the will to continue Hydreigon's mission, they will no longer threaten the fate that he has chosen to defend.

Kyurem explains his motives before he departs. He believes that the world has grown cold and wicked on account of the selfishness and distrust that pervades the hearts of Pokémon, and since the Bittercold is the very embodiment of these evil concepts, he has chosen to let the world reap its own reward: annihilation. Thus Kyurem defends the Bittercold, the instrument of the world's destruction, with every fiber of his being. Furthermore, he reveals that he believes the Bittercold will create a new, pure world once the wicked one is removed.

Once the leading pair and their allies return to the Glacier Palace to destroy the Bittercold once and for all, Munna and her gang, who are revealed to be Kyurem's underlings, try and fail to strike them down. When the player and his/her partner finally arrive at the room housing the Bittercold, Kyurem descends from the sky once again, ready to end their journey authentically this time. He comments on how weak the two of them alone are, claiming "In the face of so great a fate as this, you are like a soft breeze against a stone wall!" Believing the destiny ahead to be righteous and unalterable, he then attacks the two, beginning the main story's penultimate battle.

Kyurem's moves are Glaciate, DragonBreath, Slash, and Fly. These moves would ordinarily be no trouble to a veteran player, but Kyurem, being a massive dragon, is capable of hitting both heroes simultaneously with his attacks. Additionally, Kyurem is immune to most attacks while flying, and his Slash's high critical hit rate can make this a grueling battle for unprepared players.

Once Kyurem is bested, he falls to the ground. Although he still stands by the destruction at hand, he reveals that he would like to see what they are capable of. Kyurem then allows the two to continue into the Bittercold's lair, thus setting the stage for the final battle.

When the Bittercold finally falls, Kyurem saves the two by teleporting them away from the Glacier Palace, which is mere seconds away from falling to the ground. He expresses his gratitude for their bravery and commends them for having the conviction to save the world despite the opposition he posed. Deeply impressed by their valiant efforts, he teleports them and their friends back to their home next to Post Town.

Kyurem, in all of his forms, can be fought again by accepting a "Legend of the Mysterious Ruins" challenge request after completing the Worldcore dungeon. Kyurem reappears at a place known as Hoarfrost Tower. His alternate forms appear at another location called Turbulent Tor.

Super Smash Bros
Kyurem, in it's base form, is set to appear in the upcoming game; Super Smash Bros 4, as one of the Pokémon that'll emerge from a Pokéball. When Kyurem emerges from the Pokéball, it will use the move Glaciate, dealing a heavy amount of damage, and freezing the enemies.