Currently, on patch 10.14, Karthus has one of the highest win rates in Top, Jungle, Mid, and ADC role.
Karthus has been one of meta jungle picks for most of the Season 10, because of his fast jungle clear. His pick rate might not be super impressive but he was maintaining a fairly good win rate. However, Riot did nerf his movement speed in patch 10.9 in order to make his jungle clear a bit slower.
With that movement speed nerf Karthus’ win rate dropped to 48% in patch 10.9 from around 52%. Many players were not happy with Riot Games as Karthus was bad in both jungle and mid lane. Players were complaining to Riot Games to increase his movement speed as he basically had movement speed lower than Yuumi.
After all these complaints, last month, Riot Scruffy shared their goals for Karthus, where they mentioned: “bring mid Karthus back into a more viable position and give us the levers to tune both mid and jungle more easily in the future.”

Following up on their goals, Riot gave some massive buffs to Karthus on patch 10.14 focusing on his Mid lane stats. They increased his base health, reverted his movement speed nerf, gave buff to his Q and E while reducing his damage against jungle monsters.
Riot’s intension was to bring back Karthus in the mid lane but it seems like they kinda overdid with the patch 10.14 buff. Currently, on patch 10.14 Diamond+ Elo, Karthus has the highest win rate in Jungle, Mid lane, and ADC according to u.gg while having one of the highest win rates in the Top lane as well.
Even with all these changes, Jungle is still his primary role based on the pick rates. And on Diamond+, Karthus currently has a 53.82% win rate with a 6.6% pick rate which is the highest win rate among any other junglers. His Jungle win rate in Diamond 2 – Master Elo is around 54% as well.
Based on the pick rates Mid lane is his second most played role. Even on Mid lane he currently has a 53.75% win rate with a 17.0% ban rate which is also the highest win rate in the mid lane. And from Master – Challenger Elo Karthus also has an astonishing 55%+ win rate as well.
Karthus in the bot lane has to be one of the most broken things in patch 10.14. Even on Reddit a lot of players are discussing how obnoxious Karthus is in the bot lane. His win rate also reflecting on how overpowered he is in the ADC role, as currently in Diamond+ Elo, he has a massive 57.84% win rate. He also has a similar win rate in the Master – Challenger Elo as well.
Although his pick rate in the Top lane is fairly low, according to lolalytics, Karthus has around 52.47% win rate in the Top lane as well.
Many players are already complaining about the current state of Karthus on patch 10.14. And some of them think in order to balance Karthus, Riot need to remove him from the jungle and then balance him based on solo lane stats. Patch 10.15 balance changes are already out, so if Karthus continue to dominate like this he will definitely get some major changes in patch 10.16.