Background Information - Kyurem, the Pokemon who broke the third version trend.
I always found Kyurem to be an interesting concept as the third member. Whereas Reshiram and Zekrom represent truth and ideals, Kyurem represents an emptiness that desires to be complete, hence Black and White Kyurem. However what's most interesting is that everyone was expecting a Pokemon "Grey" version but instead GameFreak broke the trend with Kyurem and instead of getting enhanced versions, we got something much more amazing, sequels. Not only that but players for the first time got to witness the terrifying power of a legendary not through some villainous explanation but by action as Colress's "Kyurem Cannon" succesfully froze Opelucid City. It's even more terrifying in Pokemon Generations where you actually get to see it's citizens frozen alive. In fact Kyurem's most famous appearance is arguably Pokemon Generations, especially when fans started making memes about N shocked about how Pokemon can fuse. In the anime canon, he's seen as the strongest dragon-type and the one that all dragon-masters fear due to it's control over ice, testing Keldeo's courage as a warrior. Whether you thought the movie was bad or not, you have to admit he was pretty intimidating when this massive dragon hopped on the train like it was nothing. In the Adventures canon, this Kyurem is more faithful to the games as it desires to be complete, as in it wants to do absofusion with Zekrom and Reshiram no matter what and this makes him quite the dangerous player as he can render these powerful legendaries useless once he has the DNA splicers. Not only that but unlike the games, Colress uses Kyurem to freeze multiple cities rather than just Opelucid. However what's interesting is that the games never shown how Team Plasma got Kyurem and it is here in the manga that an excited Colress battles and outsmarts Kyurem, living up to his reputation as one of the strongest trainers in the game and Adventures canon.
Well-Known Trainers who caught or befriended Kyurem
Kyurem - Ghetsis (Games, Adventures, Generations)
Kyurem (Imprisoned) - Colress (Games, Adventures, Generations)
Kyurem Special - He severely needs a buff.
Kyurem
Item: Choice Scarf/Choice Specs
Ability: Pressure
Nature: Timid Nature (+ Spe, - Atk)
EVs: 252 Sp. Atk/252 Speed
Ice Beam/Blizzard
Draco Meteor/Dragon Pulse
Earth Power
Focus Blast
So Kyurem is a bit of an underpowered legendary. It has an impressive physical attack and yet practically no good physical moves to support it and it's signature move "Glaciate" is at a low 65 BP that can slow down opponents. Your probably thinking, they probably just did that to balance a buffed up Icy Wind. Well then how do you explain the 140 BP Freeze Shock and Ice Burn for his buffed up counterparts? You really have to wonder what the heck is going on with the GameFreak's Devs into designing this Pokemon. Although one could say that Black and White Kyurem are the buffs, still doesn't change the fact that the original Kyurem is severely underpowered, especially with that ice-typing. Anyways, at best, he can be a special attacker to reckon with and with hail, he is arguably the best Blizzard user outside of well... Black & White Kyurem.
Kyurem Black
Kyurem Black
Item: Icium Z/Life Orb/Leftovers
Ability: Teravolt
Nature: Naive Nature (+Spe, - Sp.D)
EVs: 252 Atk/252 Speed
Freeze Shock
Fusion Bolt
Draco Meteor/Outrage
Earth Power/Ice Beam/Focus Blast/ Roost
So you know how I said the original Kyurem needed a severe physical buff? It's the reason why Kyurem Black is considered a "mixed attacker" in the first place, not because it's one of it's best advantages but because it's forced to due to limitations. Anyways it's pretty much your basic wallbreaker but some may opt for Icium Z due to Freeze Shock's 2-turn charge. You can go for choice band however but I wouldn't recommend it due to a lot of bulky water types that can play around with it, like Toxapex.
Kyurem White
Kyurem White
Item: Icium Z/Life Orb/Leftovers
Ability: Turboblaze
Nature: Timid Nature (+Spe, - Atk)
EVs: 252 Sp. Atk/252 Speed
Ice Burn/Ice Beam
Fusion Flare
Draco Meteor
Earth Power/Ice Beam/Focus Blast/Roost
Same as Kyurem White only a powerful special attacker with more freedom of choice. So much freedom of choice that you may not actually want to use Ice Burn + Icium Z unlike Kyurem Black who is more reliant on it.