Upon dying, Karthus enters a spirit form that allows him to continue casting spells for 7 seconds.
Q - Lay Waste
Karthus unleashes a delayed blast at a location, dealing damage to nearby enemies.
W - Wall of Pain
Karthus creates a passable screen of leeching energy. Any enemy units that walk through the screen have their Movement Speed and Magic Resist reduced for a period.
E - Defile
Karthus passively steals energy from his victims, gaining Mana on each kill. Alternatively, Karthus can surround himself in the souls of his prey, dealing damage to nearby enemies, but quickly draining his own Mana.
R - Requiem
After channeling for 3 seconds, Karthus deals damage to all enemy champions.