Upon dying, Karthus enters an immobile spirit form, which allows him to continue casting spells for 7 seconds. During this time, his abilities cost no mana.
Lay Waste
Range: 875
Cooldown: 1
Cost: 20 / 26 / 32 / 38 / 44 Mana
Active: After a 0.5 second delay, Karthus blasts a target area at the cursor's position, dealing magic damage to every enemy in the area. The damage is doubled if it only hits one unit.
Active: Karthus creates a wall between 2 obelisks at target position for 5 seconds. Enemies who pass this wall have their movement speed reduced by a large amount and their magic resistance reduced by 15% for 5 seconds.
Toggle Off: When Karthus kills a unit, he restores mana.
Toggle On: Karthus surrounds himself with the souls of his victims, draining his mana to deal magic damage to all nearby enemies each second.
Mana Restored: 20 / 27 / 34 / 41 / 48
Magic Damage: 30 / 50 / 70 / 90 / 110 (+ 25% AP)
Diameter of AoE: 850
Requiem
Cooldown: 200 / 180 / 160
Cost: 150 / 175 / 200 Mana
Active: After channeling for 3 seconds, Karthus deals magic damage to all enemy champions regardless of their position on the map.
3150 or 
790
