Kyurem is a gray and blue, bipedal Pokémon of indefinable but seemingly draconic basis. Kyurem has a blue head and snout and has yellow eyes without pupils, a pair of pointed light bluish horns on its head, and a yellow crest on its skull that is bioluminescent. Three pointed teeth jut out the bottom of either side of its jaws, which are frozen shut by the ice covering its head. Its long, gray neck has lines running around its whole body, legs, arms, and tail. It has two arms, each with its claw, and each arm is joined together by its oddly shaped blue wings, which are believed to be used for flying and storing cold air. Each wing has two spikes of ice that are also bioluminescent. The ice covering the wings can break, revealing gray tendril-like appendages on Kyurem's back.

The right side of its body seems to be damaged in some way, as the wing and horn on its head on that side are shorter; the right side of its head also has a spiked edge near its jaw hinge that is absent from its left. Its legs are somewhat slender and have three sharp ice-like claws on each enormous foot. Its tail has three blue conical spikes on its tip, and appears to be some sort of propulsion device or a container of energy; exactly what it is based on is unclear, but it may be a damaged turbine.

Kyurem generates powerful, freezing energy inside itself, but its body becomes frozen when the energy leaks out. By keeping its body frozen, the cellular structure will remain stable. It is said to have a power that exceeds that of and ; however, this power is kept at bay by the extreme cold. Kyurem can transform both Rehsiram and Zekrom back into their respective Dragon Stones by using its tendril-like appendages. Due to an old legend, it may be assumed Kyurem may be hostile towards Pokémon and humans, due to the fact it supposedly ate them if they were found outside at night. In the manga, similarly to Reshiram and Zekrom, Kyurem is somehow capable of flying even with its frozen wings. It is said to be an extraterrestrial Pokémon, according to folklore. According to the anime, Kyurem is considered one of the strongest Dragon-type Pokémon in the world. Kyurem is powerful enough to cover an entire region in which it resides in ice, potentially freezing it. Kyurem loves Kyurem Treats made by Snacksworth, who once encountered it in the past.

Forms
Kyurem has two alternate forms: White Kyurem and Black Kyurem, which are formed by combining with Reshiram and Zekrom, respectively, sharing many aspects of their designs with them. It can use Absofusion on their respective Dragon Stones to change to White or Black Kyurem. The reason for this is due to Kyurem retaining the gene of the other dragons which allows said fusion. As a result, Kyurem also shares Reshiram's or Zekrom's beliefs in truth or ideals, respectively, when fused with either of the two dragons. In Kyurem VS. The Sword of Justice, Kyurem can also change into Black Kyurem or White Kyurem without fusing by channeling the powers of both Reshiram and Zekrom it has within itself.

White Kyurem
White Kyurem resembles a hybrid version of itself and Reshiram. When transformed into White Kyurem, its legs are just like the original, but shorter, and the middle toe becomes ice. As White Kyurem, it has some extra icy details on the legs. Its tail resembles that of Reshiram but is attached to the body with three gray parts of the skin. The tail is capable of movement and contains four holes. They are horizontal on White Kyurem. White Kyurem's torso is slimmer Its shoulders are covered in 'squares' of ice with two pins protruding from each which can come out and 'plug into' the aforementioned holes. As White Kyurem, it has thin arms with two rings and three claws each, wings between the rings on its forearms, and its right arm and wing are frozen. Its neck is the same shape but becomes upright due to White Kyurem using Reshiram's fur.

The ice covering Kyurem's upper jaws has partially disappeared, allowing it to move its mouth. During a battle, White Kyurem enters Overdrive mode, and tubes sprout from its back to its tail. In White Kyurem's case, the ends of its hair and wings become fiery and its tail acquires fiery highlights.

White Kyurem can use both the power of fire and ice due to fusing with Reshiram. White Kyurem can fly using its wings and the jet engine-like tail. Due to Reshiram's influence, White Kyurem firmly believes in truth. Due to foreseeing a world of truth, it will fight to protect said future for both humans and Pokémon.

Black Kyurem
Black Kyurem resembles a hybrid version of itself and Zekrom. When transformed into Black Kyurem, its legs are just like the original, but shorter, and the middle toe becomes ice. Its tail resembles that of Zekrom but is attached to the body with three gray parts of the skin. The tail is capable of movement and contains four holes: they are vertical on Black Kyurem. Black Kyurem's torso is bulkier. Its shoulders are covered in 'squares' of ice with two pins protruding from each which can come out and 'plug into' the aforementioned holes. As Black Kyurem, it has Zekrom's arms, but they are more muscular and without wings, and its left arm and wing are frozen. Its neck is the same shape but becomes upright due to Black Kyurem using Zekrom's skin.

The ice covering Kyurem's lower jaws has partially disappeared, allowing it to move its mouth. During a battle, Black Kyurem and White Kyurem enter Overdrive mode, and tubes sprout from its back to its tail. In Black Kyurem's case, parts of its right arm and the tip of the horn on the back of its head turn blue, while its tail lights up with electricity.

Black Kyurem can use the power of both electricity and ice due to fusing with Zekrom. Black Kyurem can fly using an anti-gravity field through its generator-like tail. Due to Zekrom's influence, Black Kyurem firmly believes in ideals. Due to foreseeing an ideal world, it will fight to protect said future for both humans and Pokémon.

(Source: Bulbapedia)