The top champions out of lane to counter Karthus include Kalista, Lucian, and Aphelios. These champs are all great at countering Karthus with win rates over 62%. Even if these Karthus counter picks are not picked in the same position as you, it's not smart to choose him into these matchups. They will often crush Karthus.
Conversely, if the opposite team picks either Taliyah or Xerath, you should strongly think about choosing him, as he easily wins against these champions with win rates over 54% against each ofthem.
Tentar dar pick-off em Karthus antes de uma teamfight porque ele é excelente em mitigar danos e estar no centro da batalha.