Karthus Build Guide by Aqua Dragon
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+9 Adaptive (5.4 AD or 9 AP)
+8 Magic Resist
- Moves quickly; easily sticks to opponents
- Incredible mana sustain during laning
- Powerful initiator
- Strong early kill potential
- Great roam during laning phase
- Weak waveclear
- Devours mana rapidly during fights
- No inherent tankiness
- No inherent health sustain
- Low AP; ultimate is weak
Karthus is most known for amassing massive AP, sacrificing themselves into the fray to do massive burst damage with Defile, and cleaning opponents with a half-health chunking Requiem. However, it turns out Karthus is able to viably become a more sustained-damage tank that trades off the chunking power of the ult to become a higher-ranged Singed during teamfights.
This is possible because Karthus only has a great AP ratio on Requiem. It is fairly lackluster on Lay Waste and Defile. The AP ratios of each spell are:
Lay Waste (Multiple): 0.3
Though the 0.6 scaling on Lay Waste is nice, it only applies when hitting a single target. This is largely only feasible during laning. In teamfights it's far more likely to only get multi-hit Lay Wastes unless Karthus is chasing someone down.
To be fair, both Defile and Lay Waste hit every second, making the low AP ratio more valuable. But also to be fair, the base damage is also hitting every second. In reality, it's less about the AP ratio, and more about the Scaling to Base ratio. To illustrate the importance, let's compare two Karthuses. One with 300 AP and one with 0 AP.
With Defile active for 5 seconds, at rank 5, the 0 AP Karthus will deal 550 damage. the one with 300 AP will deal 850 damage. This is only a 300 damage difference, meaning a Tank Karthus would only have to live for 3 extra seconds compared to AP Karthus to make up the difference. So while the up-front damage AP Karthus can deal is much higher, Tank Karthus will deal the same amount of damage over time by living in fights longer and freely positioning
This means that getting AP is primarily useful for Requiem, not for the other spells. However Requiem is on an impressively long cooldown and there are an amazing number of ways to nullify its damage. Instead of banking most of the damage into Requiem, could power be transferred away into the rest of the kit? Tank Karthus answers this question with a resounding yes.
Tank Karthus does this by transforming into an Artillery Tank that abuses the base power of Defile. A standard AP Karthus tries to abuse the scaling on single-hit Lay Wastes to do damage, but this creates unreliability in the damage output. In addition, maxing Lay Waste first prevents the surprising power of Defile from being abused.
Each level of Defile is on par in damage with its equal-level Lay Waste counterpart. This is to say, a Level 3 multi-hit Lay Waste does non-guaranteed 80 damage. A Level 3 Defile does 70 largely-guaranteed damage in an AOE. Thus, maxing Defile first is like hitting your opponent with a non-amplified Lay Waste every second. This isn't strictly true and has nuance, but the principle is the point.
There's good reason Defile isn't used this way. Its high mana drain is, well, draining. In addition, putting yourself into range of its use is extremely dangerous for the fragile Karthus.
This is where Tank Karthus moves in (literally). Because Tank Karthus doesn't have to focus on AP items, they are able to focus more heavily on maximizing a mana pool and building survivability to make amazing use of Defile. This is combined with high mobility/slows from Dead Mans, Randuins, Ghost, Wall of Pain, and Exhaust to make Karthus stick to the enemies and whittle them down Singed-style.
Because of this, you will often end up doing the most damage out of everyone in the game, even comparable to a full AP Karthus. The damage will be more sustained by comparison and suffers the disadvantages of the damage style, but the presence in fights still demands respect.
Tank Karthus might be a tank, but they still have some disadvantages at top lane compared to melee tanks.
First, Teleport is much more mandatory at top, which prevents running the excellent Ghost / Exhaust combo. It's possible to avoid Teleport, but this makes it hard for Tank Karthus to deal with the constant pushing due to being much more dependent on mana than traditional top laners. Worse, Teleport falls off in utility later into the match since Tank Karthus lacks raw pushing power.
Second, Tank Karthus is pretty reliant on mana to deal damage, which makes it difficult to kill tankier targets with Defile. Against squishy top laners like Teemo, this disadvantage is much less pronounced.
Finally, Tank Karthus enjoys roaming around on foot and setting up for teamfights, which are both more optimally geared for mid lane than the top lane. Fights are more likely to occur at dragon, and Mid offers two different lanes to roam to instead of just one.
Tank Karthus can still be functional at top lane, but I prefer it at mid to realize its full potential.
Karthinking About Runes
Aery adds significant lane presence and is the sole reason you go with Sorcery primary. Phase Rush gives up too much laning power.
Manaflow's extra spells keeps Karthus alive longer than Orb's pitiful shield.
Celerity because the other options suck for Tank Karthus.
Scorch provides just literally enough damage for Tank Karthus to win trades early on, since otherwise, it's frequent to be just a single spell too little from finishing off a target.
Conditioning is why you're going Resolve. It's 15% more effective HP.
Unflinching has great synergy with Tank Karthus' summoner spells while the alternatives don't do enough to compete.
Flat AP, Armor, and Magic Resist
A standard tank package to add plenty of durability. Defensive stats can be adjusted depending on matchups.
For a primary rune tree, Sorcery seems like an odd choice. Why not an option with more utility or tankiness?
There are some nice keystone choices in other pages whether it's Domination's Predator MS bonus for engages, Inspiration's Unsealed Spellbook for engage versatility, or even Resolve's Guardian for more tankiness during teamfights.
It all boils down to one thing:
Tank Karthus can't do their job if they can't compete in lane, and after ample testing, it was found that Aery is integral to competing.
This is really something that only experimentation can show. I've tried all the other options, fiddled with the build order tremendously, and generally tried as hard as I could to avoid just relying on raw damage. But in the end, Tank Karthus' laning phase is gimped too hard by anything other than Aery.
It's a shame then that Resolve becomes essentially mandatory as the secondary rune tree. The bonus MR and Armor are needed because Karthus has no inherent defensive bonuses.
This does mean you don't get access to any of the cooler runes that would otherwise synergize awesomely, but that's just the sacrifice that has to be made when delicately balancing durability and damage.
Soul Build Order
Tank Karthus' playstyle favors stickiness and abusing Defile. This means Mana, mobility, and durability are top priorities for Karthus.
AP is not the goal of the build.
Doran's Ring is excessive, so start with Sapphire Crystal.
But if you can massively bully the enemy laner, go for Corrupting Potion.
Prioritize the Sapphire Crystal.
Build one of these defensive choices to help you in lane.
I would love to give any of these options a glowing recommendation since they're all a ton of fun to build, but sadly they all don't offer enough raw durability to justify the purchase.
Tank Karthus is already on the fringe of balancing durability and damage. These options skew too much in the damage / utility / durability direction that Tank Karthus cannot do an effective job. The build is about a balance, and these throw that balance off.
In the early game, your goals are to
- Farm waves from a distance
- Dive opponents regularly with Defile and force summoner spells
- Replenish mana between these attacks with Defile's mana regen
Bully Hard: Don't let up! Make the opponent suffer for every minion they wish to get next to.
Abuse Defile's Mana Refund: Each dive is heavily mana intensive. Early levels in Defile will provide a quick way to get more mana as you prepare for the next tackle.
Farm with Autos: Using Lay Waste to farm will not return nearly as much net mana as farming with autos, so avoid relying on it when you can.
Abuse Aery: Time your Lay Waste harass with Aery to maximize the poke damage. It adds up exceedingly fast.
Roam Often: You can start roaming very early on due to the powerful engage that Ghost provides. When your opponent has left lane, run over to other lanes and use Ghost to ambush unsuspecting opponents.
Don't Overly Rely on Lay Waste: It's sometimes better not to use Lay Waste during defile tackles, as the mana cost expends a second of Defile's time. Unless you know for sure that you'll land the hit, let Defile do the brunt of the work.
Autoattack During Tackles: At early levels, the autos will nearly as much damage as Lay Waste!
Don't Level Up Wall of Pain Until 7: It has an exorbitant mana cost and the slow it provides isn't as strong as simply getting earlier points in Lay Waste and Defile.
As the laning phase ends, you will start taking on a more aggressive role.
- Initiate fights with Ghost, Wall of Pain, Exhaust, and Randuins.
- Pick a target in the fight and stick to them
- Chase down lonely opponents and kill them
- Use Requiem to clean up easy kills
Dive Headlong: You are the one who decides when fights happen due to the enormously powerful initiation. Lead the charge; you decide when it's time.
Disengage, then Ult: Opponents who barely escape from your defile tackles can be shot down with Requiem. Take note however that Tank Karthus' Requiem is not too strong. Keep tabs on its base damage and use that number to figure out when it's time to ult.
Preemptively Ult Often: It is often better to just use Requiem preemptively instead of trying to execute targets with it. Notice a fight happening in another lane? Just ult anyway. Otherwise, trying to execute targets will usually just leave Requiem on cooldown for half the game.
Duel Regularly: Your dueling power is fairly respectable. If you see someone extending too far to push or too far in your jungle, use your superior mobility with Exhaust to defile them down.
Use Full Defile Range on Melee Champs: You move pretty fast and are tanky, but that's no reason to take free hits. Try to skirt melee enemies at the edge of your defile instead of always standing right next to them.
Get Close to Ranged Champs for Aery Procs: Try to stay especially close to ranged targets when using Defile since this will allow Aery to refresh multiple times over the course of a fight. The closer you are, the faster it refreshes.
Watch Your Mana: Once you're out of mana, you're spent. You have no real mana regeneration outside of lane. Be cautious of your mana bar to make sure you won't overexert yourself before battles are truly done.
You retain a similarly sticky role as the game reaches its conclusion
- Build defensive items for the situation
- Make picks on lonely opponents with your mobility
- Try to attract the attention of as many opponents as possible in fights
Lead Fights: Continue to start fights when you see openings. You remain the dictator of when fights begin.
Consider Thornmail: Thornmail is especially powerful on Karthus. It's easy to get into close range of ADC's. Once Thornmail nullifies their lifesteal, their death becomes guaranteed, especially with an Exhaust. If you can force the ADC away by yourself, you can gain an immense fighting advantage for your team.
Spam Lay Waste: Your Lay Waste will start packing a bit of a hit now. Feel free to spam it for offense, though be mindful of your mana.