Where it appears this weekend

Five-star raidsSunday, November 15, 10:00 a.m. - 6:00 p.m. local (Saturday's slot belongs to White Kyurem + Zekrom).
FusionKyurem + Zekrom + 1,000 Fusion Energy. The energy drops from Black Kyurem raids - no raid, no fuse.
Not a wild spawn. Black Kyurem is a raid boss, not a mighty Pokemon - stockpile free raid passes (up to 3 per day from Gym photo discs this weekend) and queue with a group.

Best counters (Fighting, Rock, Steel, Dragon, Fairy)

CounterMoves
Mega LucarioForce Palm + Aura Sphere
Metagross / Mega MetagrossBullet Punch + Meteor Mash
TerrakionDouble Kick + Sacred Sword
DialgaMetal Claw + Draco Meteor
Zacian (Crowned Sword)Metal Claw + Behemoth Blade
Shadow ConkeldurrCounter + Dynamic Punch
ExcadrillMud-Slap + Scorching Sands

Best movesets

UseMoveset
Raid attackerDragon Tail + Freeze Shock (Ice) or Outrage (Dragon)
Master LeagueShadow Claw + Freeze Shock and Outrage (Master League)

The strongest Ice-type raid attacker in the game when it runs Freeze Shock, and a premier Dragon attacker too. Requires fusing Kyurem with Zekrom using Fusion Energy earned from its raids.

Fusion & evolution

Kyurem + Zekrom + 1,000 Fusion Energy → Black Kyurem

Fusion is reversible - unfuse any time to get both Kyurem and Zekrom back with the energy already spent. A fused Black Kyurem keeps the Kyurem's IVs and shiny status: fuse a shiny Kyurem and the result is a shiny Black Kyurem.

FAQ

Can Black Kyurem be shiny in Pokemon GO?

Yes - shiny Kyurem is released, and fusing a shiny Kyurem produces a shiny Black Kyurem.

Is Black Kyurem worth raiding?

Yes - it is the best Ice raid attacker in the game with Freeze Shock and a top Dragon attacker. The Fusion Energy you earn is the bottleneck, not the boss itself.

What is Black Kyurem weak to?

Fighting, Rock, Steel, Dragon, Fairy - bring Mega Lucario, Metagross or Terrakion.