League of Legends Karthus players will find him to be a complex champ to build out properly. You'll find that his build varies when he is playing against either diversified or homogenous team compositions, indicating you should not follow the same Karthus build every single game of League of Legends
The most important items to use in your champ's build include: Tempesta di Luden, Copricapo di Rabadon, and Ombrofiamma. Players who included these items in their builds had a higher win rate than those who worked towards other Karthus builds. Moreover, if you are fighting a well-mixed enemy team comp, you should really consider grabbing Karthus the Dominazione, and Precisione runes. In recent games, he won the largest fraction of his matches when built with these runes.
We came up with our Karthus build guidance by examining 15.381 recently ranked League matches with him selected. We only propose the best winrate Karthus builds that were built by ranked gamers enough times for us to advise them. With so many rounds in our data, we are quite confident in our suggested builds.