Secret OP Mid Counter to ADC Kog That No One Plays

The answer is always Karthus!

You can't dodge his ultimate and it's going to chunk any squishy. With Rylai's and Liandry's (yes, really), he will also melt that frontline which is supposed to protect Kog. The ult. can even be used as an engage tool near objectives since it will do massive damage and it will be very hard to stop an engage with the massive slow from Rylai's on 5 people. His AoE damage is also so high that the traditional gameplan for Kog of grouping mid-late becomes very tricky.

Why not Zed, LB or Talon, you ask? Those certainly can work but they involve much higher risk to get to Kog and can't really deal with the protective champs usually drafted to save him. They simply lack effectiveness vs beefy frontlines with hard engage. Moreover, it's much easier to siege vs them due to the lack of waveclear. Karthus works so well vs him that if you want, all you have to do is flash near him and even if you die instantly, you create a zone that makes it impossible for Kog to get to the rest of his team and output DPS. This matters a lot more than vs other ADCs because Kog has windows of power rather than consistent damage like Vayne. If your death simply times out his W without unleashing it on the team, he will be pretty much useless during that time.

We've already seen several Rumble jungles, it's time to pull out the Karthus.