Karthus/Strategy

Skill usage

 * Sometimes it can benefit to die a strategic death, by rushing into a group of enemies and casting  the enemy will focus you long enough for your team to initiate without affecting your chance of winning a team fight, as  can cast his spells even after dying.
 * You can also activate right before dying to let  tick even longer. You can also use  when dead to mow down the person who killed you.
 * His passive allows him to cast spells while dead. Abuse this every time you die and punish any who remain near your corpse, casting if not already used and endlessly casting . This may actually get you a kill.
 * When focusing on harassment, try placing where it will hit the champion, but not the minions. This way, it will deal double damage.
 * is a great harasser. Use your to zone your enemies.
 * can be used to scout brushes since it reveals a small area around where it is cast. Since the skill has a low base cost, this can be used to scout brushes frequently.
 * is very strong at farming minions and harassing enemy champions.
 * Taking 1 level of gives you a slow allowing you more time to cast  on fleeing enemies, as well as deterring attempts of harassment, even at their towers. In later game it is useful in team fights, thanks to its magic resistance debuffs. With this spell,  can actually be a very good ganker, as it slows and allows his teammates to deal more damage.
 * at higher levels can mow down creeps by standing next to them or walking past them for just 2 seconds. If given free rein or adequate protection from enemy champions, this can turn the tide of a battle very quickly or cement a teams victory.
 * Ask your allies to help point out when you should use to get kills in different lanes, or alternatively, alert your teammates when you are about to use it. However, be sure to keep your eye out for action elsewhere on the map; you may be able to help someone when they otherwise wouldn't have time to type for help.
 * Before using to kill a retreating enemy, consider the shield/heal/defensive abilities and items of the enemy team; at endgame, it is usually more important to have an ultimate up than to force enemies to heal.
 * During laning, it may be more beneficial to attack the caster minions in the back and to kill them than to harass an opponent. If you find yourself being outlaned by the enemy, pushing them back and stacking up on your own minions can help control them and keep them away from your tower.
 * If your team can effectively distract the enemy, can actually be a very effective pusher, as the sheer speed at which he can consistently clear minion waves allows him to push his team's minions to a tower and destroy it in a short amount of time.
 * highly benefits from the buff, giving him increased mana regeneration and reduced cooldowns for all his spells, allowing a focused AP build.
 * can be used mid-game before a major offensive is launched to weaken all enemies, making them easier to kill.
 * and are useful summoner spells, as  often needs mobility in order to be an asset to the team.
 * It is possible to jungle using with the proper runes and/or masteries. To get the blue golem rune, use  only on the blue golem (missing the smaller monsters). This way, you will deal double damage to only the golem.
 * Be careful of when to use due to your ability power and the enemies magic resistance.
 * Using will deal damage every second to your opponent after activation. With no cooldown reduction, it has a 0.5 second cooldown on both ends (activating and deactivating), making it deal the same damage as just leaving it toggled on. With any cooldown reduction, however, you can increase your damage by rapidly toggling on and off. At 40% cooldown reduction, you can effectively deal damage once every 0.6 seconds, instead of once every 1 second, for 1.67 times as much damage.
 * Both slow and stat reduction go through.
 * can be a viable tool to saving an ally champion's life due to its movement speed reduction. Use it to give your allies a chance to get away if they are running from a pursuing champion.
 * On Dominion, can work as a potent defender in bottom lane (between the Boneyard and Quarry), thanks to his potent zoning, ability to easily defend his point until reinforcements can arrive via his passive, damage aura via, and  poke, and abilty to have a global presence via . However, he is very vulnerable to ganks if overextended.
 * If you're taking as a top laner on Dominion (between the Drill and Refinery),  can prove quite useful as an initiation tool for turret teamfights (especially at the Windmill), as it increases the damage all your allies deal while slowing the enemy. (If placed right, it can even reveal their brush!) By taking levels at 3, 4, 10, and the remaining two between levels 11-18, you can become frightfully efficient at helping your allies cap points. As such, taking  to further improve your initiation can prove valuable.
 * is very good at interrupting captures via and.
 * Notice that is very good at medium range, however he is easily countered by champions who can attack him from a very long range like, for example,.

Build usage

 * Due to, the enemy team will likely build some magic resistance. Building magic penetration items such as will help pass through their defenses.
 * can enable you to regain health quickly with or, especially with enemy minions around.  also gains full spell vamp when only used to attack a single enemy.
 * When played as more tanky build, consider as a top-priority item. Its passive provides slow for all your spells, but especially for, which you can use to kite enemy with terrifying effeciency.
 * On either lane for Dominion, has a great deal of utility. Not only can it be used to secure kills, but it can also slow via, reveal all enemies via , butter up enemies for your teammates from afar, or simply work as a global capture interrupter.
 * Try building tanky on Karthus as you will try to stay in the teamfight with your on and spam.
 * Building an is a strong choice for Karthus as  can quickly build up the Archangel's staff's passive.
 * has nice synergy with . You can Lower the target's magic resistance by 15% and ignoring 40% of it, ending up in 49% when combined.
 * Since the now provides percentual magic resistance reduction, it can no longer decrease it below zero. Flat reduction from  has less synergy, but it can still be useful against champs with lower magic resistance.
 * As mentioned previously, Karthus can be played as suicide initiator. Build him fully offensive with items such as and  to maximize your damage output.
 * can be viable even in this build. You can kill and assist easily with, being able to maintain more stacks even with your death.

Countering

 * Playing against can be extremely frustrating, as avoiding death with a small amount of health left is nearly impossible due his . If you find yourself having trouble with an enemy, buying a  can offer at least some protection to his ultimate. If you are a caster and wish different/more protection, grabbing a  earlier than you normally would can save you on many occasions. If you are an AD-based champion and wish for some additional protection, a  or  can block 250 or 400 magic damage respectively from his ultimate if he takes you below 30% health. Beware however, those items aren't as reliable as.
 * is a good counter to Karthus's ultimate during the early and mid game. It costs only a fraction of the other items which would normally be used to counter.
 * Always remember, especially during team fights, that can continue to cast spells while he's dead without the cost of mana. When engaging his team, kill  first, then retreat out of his attack area before continuing the fight.
 * When in the midst of a team fight, it may be difficult to notice the attack animation of his . Be wary of this if you are playing a squishy character and/or have little magic resistance, as damage output is steady and deadly.
 * Also, do not underestimate the tick on his . It is DoT, so it may not be noticeable at first, but its damage can be as much as 160 per second, not counting resistances, on top of his damage from.
 * Do not underestimate 1v1 potential. He may be squishy, but his killing power vastly increases when fighting stationary, single targets. If you engage him as ranged, try to stay out of his  and keep moving to avoid his . If you need to remain stationary, stay near other targets that will be damaged by his  (e.g.: Allied minions or neutral monsters) to reduce his damage output. If you engage him as melee, you should either only do so if you have the level advantage or survivability to engage him in his AoE spells and live.
 * reduces magic resistance, instead of penetrating it. This means that damage done to you by all enemies will be increased. Keep this in mind while standing in or walking through his during a team fight.
 * Some players will intentionally walk into a teamfight and die, This is rather a great strategy if  is in a situation where he will die because he can cast his spells for 7 seconds after his death allowing him to freely channel . Make sure that after you kill him, stay away from his.
 * Laning against can be challenging if you are not aware of his . Without at least one movement speed increasing item (e.g. ) walking away from your minions can be costly even while watching for 's if the  is predicting your movements accurately. To avoid the doubled damage, stand near one or two minions. That way, if  attempts to harass you with, he is either doing minimal damage to you and the minion or placing it so that you have more time to respond, as the AoE is only half as close to you. Standing in the middle of your minions is a less favorable way to reduce damage as the unit collision can more or less hold you in place while  s continually.