Not Updated For Current Season
The masteries shown here are not yet updated for the current season, the guide author needs to set up the new masteries. As such, they will be different than the masteries you see in-game.
Karthus Penta Kill
This is a great build if you like to mid with karthus and you can farm with him pretty well.
I hope this helps karthus fans and players.
Pros / Cons
-Easy to do.
-When killed in a team fight you can still be very effective with this amount of ap.