First off, I want to give credit where credit is due and say that this build was inspired by Aqua Dragon and his "Diamond Tank Karthus - Slow Death" build and is very similar. You can find Aqua's build HERE


If you're wondering "how could tank karthus possibly work?" the answer is hidden in his AP ratios and the base damage of Defile (E). Karthus actually has pretty bad AP ratios besides his ult (70% AP ratio). His Q only has a 35% AP ratio unless you hit an isolated target in which case the ratio is 70%, however hitting consistent isolated Qs is an unreliable source of damage and often isn't really possible in team fights where multiple targets are grouped together. Defile (E) has a 20% AP ratio which is pretty bad, however the base damage that increases with Defile's level is very good. With no extra AP, Defile will deal 110 (+20% AP) magic damage per second or 27.5 (+5% AP) magic damage per tick (each tick is 0.25 seconds) at max rank. This means that you are able to build Karthus very tanky while maintaining the surprising damage that Defile provides both in lane and in team fights. Defile is very mana hungry but the runes in this build, coupled with a couple specific items helps mitigate that as long as you are toggling Defile on and off when you should be.

Play safe early, poke and farm with Q. Once you have some decent components or your first full tank item relative to the champ you are laning against, don't be afraid to take long trades with your E. Just walk forward, turn your E on and try to hit as many Qs as possible, you will be surprised how much damage you do and how healthy you remain after these fights with champions that would normally roll over Karthus in the early game. Keep an eye on your mana, always try to keep enough mana to be able to shove a wave so you have an opportunity to back for items or just to regen your mana. Shoving waves is easy, your E will melt waves if you max it first. Outside of lane phase, you want to be the frontline for your team. Communicate with your team so they know how to play around a tank Karthus. Go in and start trying to stick to people with your E on, be sure to toggle your E on and off when required. The enemy team will likely dogpile onto you, which is good for your team because they will waste a ton of their cooldowns on you, take a bunch of damage from your E and Q, and then if you're still alive when your team follows up it should be an easy fight. If you die after the enemy team jumps on you, you will still have made them waste their cooldowns on you, you have chunked them all with your E and Q, and then you still have 7 seconds of Death Defied to continue dealing damage, all while Last Stand is increasing your damage by 11%.

I will say that the one big downside to this build is the fact that your ult will do very underwhelming damage. You can still get some cheeky ult kills if an enemy is literally 1hp and running for their life afer somwhow escaping a losing fight, but mostly your ult will turn into a gold generation tool. If you see a fight happening across the map and it looks like your teammates will come out on top, ult. The damage won't help much, however you will secure assists this way, and the extra gold that generates is great.

It takes a while to get the hang of Tank Karthus but I guarantee you, even in games when you don't feel like you've been that impactful, just look at your damage done/taken stats after your game and you will see that the impact is definitely there. You are useful all game long, even if it isn't in the flashiest way. It's also priceless watching a super confident enemy aggresivly attack you (a seemingly defenseless, squishy Karthus) at which point they have made a terrible mistake by getting close to you. They realize they are only tickling you, and their health is disappearing at an alarming rate.