Abilities
Karthus becomes a spirit on death, letting him cast spells for a short time.
Delayed AoE blast deals bonus damage to isolated enemies.
Creates a passable wall that slows enemies and reduces their Magic Resist.
Karthus drains mana per second to damage nearby enemies, and gains mana on kills.
After a 3-second channel, Karthus deals damage to all enemy champions globally.
Guide
Play as a backline poke mage, focusing on constant Lay Waste spam and using your passive to deal damage after death. Prioritize mana sustain and ability haste to maximize your ultimate's impact.
Tips
Use your passive to keep casting abilities after death, especially Lay Waste for area denial.
Build mana items like Seraph's Embrace to sustain your high mana costs in ARAM.
Position safely behind your team and use Lay Waste to poke from a distance.
Take Ultimate Hunter rune to reduce Requiem cooldown for frequent global pressure.
Buy Zhonya's Hourglass to survive dives and continue dealing damage with your E and Q.
Combos
Use Wall of Pain (W) to slow enemies, then spam Lay Waste (Q) for damage.
Activate Defile (E) before dying to maximize area damage while in passive form.
Cast Requiem (R) when multiple enemies are low health to secure kills across the map.
Follow up a teammate's engage with Wall of Pain (W) and Lay Waste (Q) for burst.