Ah, Kyurem. The final member of the Tao trio. This form is BL due to a few major things that really hold it back: an Ice/Dragon typing, a weakness to all arena traps (which means that Rapid Spin support is almost essential), and a weakness to priority moves. Sure, its bulk is decent, but with all the weaknesses, that bulk quickly becomes worthless. That doesn't stop Kyurem from being dangerous, however; this thing is an absolute monster in hail with STAB Blizzards coming off of base 130 Sp.Attk. Here's something to put this into perspective: its Blizzard rips straight through a Dragonite's Multiscale, landing an OHKO before Dragonite can set up.
Without further ado, let's look at a few sets Kyurem can run:
Item: Choice Scarf/Specs
EV Spread: 252 Sp.Attk, 252 Speed, 4 HP
Ability: Pressure (a pity it doesn't get anything else without the other forms)
Moves: Blizzard/Ice Beam
Focus Blast/HP Fire
This set is one of the sets that makes Kyurem truly dangerous. Give it Specs if you'd like to kill everything, give it Scarf if you'd like it to be a revenge killer (although it is sadly outrun by a few other Scarf users in OU such as Haxorus, Hydreigon, and Salamence). Use Blizzard only if you have hail support. Otherwise, use Ice Beam, as it does still kill things. Focus Blast and HP Fire are for Steel types. Whichever one you use depends on your preference. Draco Meteor is for breaking down opponents, and Dragon Pulse is for late-game sweeping.
The All-out Attacker
Item: Life Orb
EV Spread: 36 Attk, 252 Sp.Attk, 220 Speed
HP Fire/ Focus Blast
The all-out attacker with the ability to switch between attacks. Outrage and Draco Meteor are wall-breaking moves. Outrage for Blissey, Draco Meteor for everything else. Ice Beam is for use against other dragons, and HP Fire/Focus Blast is for Steels.
The Substitute user (my personal favorite)
EV Spread: 252 Sp.Attk, 52 HP, 204 Speed
Moves: Blizzard/Ice Beam
This set is the one I use for my hail team (and it has served me well). The EV spread is designed to give Kyurem 404 HP, which allows it to make 101 HP Substitutes, which allows it to survive two Night Shades/Seismic Tosses. You can also use Timid nature, but I prefer Modest for wall-breaking power. The goal here is to save this variant for late-game sweeping, when all Kyurem's counters are gone, so that you can safely set up a Substitute that won't be broken by what they have left. Leftovers is essential for this set, as it gives Kyurem a semi-reliable form of recovery. Blizzard is if you have hail, otherwise, use Ice Beam. Focus Blast is for Steels (although you can also use HP Fire, it's not preferred, as Kyurem will need a bit of speed). Dragon Pulse is for a neutral attack.
A Gimmicky Set
Item: Red Card
EV Spread: 100 Attk, 156 Sp.Attk, 252 Speed
Moves: Hone Claws
A set that I've grown to not use as much due to the time it takes to set up and the amount of counters that can ruin this set. Basically the goal is to set up a Hone Claws to improve Kyurem's accuracy and attack with super-strong attacks (Blizzard, Focus Blast) without worrying about pitiful accuracy. Outrage is there for Blissey, as it does somewhat wall Kyurem otherwise.
Other options: very few. Its movepool is barren without the enhancements of Reshiram or Zekrom. You could try an all-physical set, but it doesn't work very well.
Kyurem's counters: Plenty. If you can outrun Kyurem and pack a super-effective attack, that thing will fall before you quickly. The Pokemon that commonly do this are Scarf users. To name a few that can deal with Kyurem: Terrakion (with and without a Scarf, it still sends Kyurem packing), Salamence, Haxorus, Hydreigon, and Landorus. Other counters include priority users (specifically Scizor, as and SD boosted Bullet Punch will KO) and putting up arena traps. If even Stealth Rock is up, Kyurem has a difficult time switching in and out of combat.
Overall, this is the worst form of Kyurem, but it is an absolute monster in hail that will dispose of your team should you give it that chance.