The best champs globally to counter Атрокс include Калиста, Афелий, and Самира. These are all great at countering Атрокс with win rates over 54%. Even if these Атрокс counter picks are not taken opposite your position, it's not smart to take him into any of these matchups. They will often destroy Атрокс.
Conversely, if the enemy team brings either Шако or Талия, you should seriously think about taking him, as he easily dominates these selections with win rates over 53% against both ofthem.