This guide will show how to PWN-ing with Karthus. He need alot of mana and cooldown reduction for ulti.On solo lane you can make first blood on 3 lvl. Karthus is so paper, you have to play care. Lay waste is good to farming minions.

I choosed Archangel's Staff for first item because karthus have to have 6 lvl for ulti and cant leave him lane.

Tell ur team to say when need ur ulti. You have attack last, because karthus can eat everyone when enemy attacking another player.