The only Kyurem Counter that Mono Water has.
Gen 8 SS Monotype (Water)
Walrein @ Leftovers
Ability: Thick Fat
EVs: 248 HP / 8 SpA / 252 SpD
Calm Nature
IVs: 0 Atk
- Ice Beam
- Toxic
- Rest
- Roar
Recently, some Water-type teams have dedicated a team slot for Walrein just so they don't autolose to Kyurem (specifically the SubRoost set). That's the only reason Walrein is used in Gen 8 SS Monotype: to counter SubRoost Kyurem. Sure, there are checks like Slowking who do fine vs Kyurem, but they can't directly switch into it. So, if you're looking for a Kyurem counter for a Water-type team, Walrein is it.
Ice Beam is used for Ice STAB that allows you to break Kyurem's Substitute. Toxic allows you to pressure Kyurem provided Kyurem's Substitute is broken and it spams Roost in an attempt to PP Stall Ice Beam. Rest is for healing to prevent Kyurem from breaking through Walrein. Roar is used as a "if all else fails" last resort to force Kyurem out of the field.
So, uh, yeah. A Kyurem Counter Walrein set if you need one for Water-type teams.