This guide assumes you are an advanced karthus user. It does not focus on Karthus as an extreme. But rather a sustainable hit and run champ that can wade into a team fight for a few seconds to provide the extra damage for quick aces.

With this build you are extremly vulnerable as always while playing a karthus. But with this build you can provide extreme help in the event of an emergency. This build is not meant as the carry. or as the back door specialist. With this build you become a team fight changer.

Very little magic pen means you have to be constantly watching for points to attack. Get good at reading someones pattern of movement and anticipating where you can hit with lay waste. It deals 2x damage to single units. and with defile you can farm quite quickly just last hitting minions.

Grab blue when ever possible to sustain mana. And farm as much as possible at all points in the game.

Your ult is not meant for kill stealling. It is meant to help before or after fights and when your team cannot safely get a kill. Such as if they would have to tower dive to get that last hit.