Karthus

          I tried out Karthus today, and he is pretty good. He doesn't really have much killing power if you are against someone with better range, but his ult really helps the whole team. Now start with Crystalline flask and 3 pots for lane sustain. Buy Sorcerer's shoes, Hextech Revolver, and Tear of the Goddess next. If you want you don't have to buy the Hextech Revolver, as you will be selling it later. I like it because of the spell vamp however. Karthus's Q is like a basic attack, too, so you will be healing a lot from that. Then buy Archangle's Staff, Zhonya's Hourglass, Rabadon's Deathcap, Rylai's Crystal Scepter, and Deathfire Grasp. Like I said, he doesn't have too much killing power until his build is pretty far along, so you are going to have to stay alive the whole time. If you die you will lose the edge that you need later in the game.

Karthus

Grim Reaper Karthus