LoL Karthus players will find him to be a complex character to build out properly. You will find that his build varies when he is up against either diversified or highly focused team compositions, indicating you should not select the same Karthus build every single game of League of Legends
The most essential items to use in your champion's build include: Ludens Sturm, Rabadons Todeshaube, and Schattenflamme. Those who added these pieces in their setups had a greater winrate than those who went for other item builds for Karthus. Likewise, if you are facing a well-mixed enemy team comp, you should strongly consider getting yourself the Dominanz, and Präzision runes. In recent games, he won the largest percentage of his rounds when built with these runes.
We established our Karthus build recommendations by examining 15.381 recently ranked League games with him in them. We only recommend the top winrate Karthus builds that were used by ranked players enough times for us to reccomend them. With so many matches in our data, we are confident in our provided builds.