The Cow King's first Ability is Berserk, which deals 2 Physical damage to one of your minions every turn.
His second ability is Decompose, which will remove one Structure Point from one of your Artifacts every turn.
His third ability is Shatter, which has a chance to destroy one of your Weapons or Armors every turn.
Cow King's deck consists mainly of his subjects, Cows. Most of them are very tanky, with Toughness and Resilience. Other than that, he has a lot of heals, which are powerful with his Red Buttermilk Well.
The Cowking deals 2 Physical damage to one of your minions every turn. Making it nearly impossible to use creatures with less than 3 Health! You should Use as many High-Health Creatures as you can find, and any creature with Resilience, as that will reduce his damage output.
Most of his creatures are very tanky, with Toughness and Resilience, so be sure to bring creatures and Weapons that have Execute and deal damage other than Physical!