Basically the idea of the build is a defensive way to play Karthus. Your goal is to be as annoying as possible, while covering turrets and snatching the kills of low, escaping enemies. From the levels of 1-11, you will basically be farming/defending your lane's tower. Many players will try to force and kill you at turrets, which will in turn, net you doubles/triples. The combination of Wall of Pain, Defile, and being near a turret, will really lay the hurt on any tower diving people.

The idea of this build, is to not be afraid of death. You are death, you will stand and cover the tower from 2 or 3 people, by yourself. If you die, which you probably will, you will take people down with you. The build focuses on having high damage while basically always being alive (in some form). Revive and then Teleport back to the tower you were defending, basically nulling any onslaught of players, while your team can push their lanes. You're holding off 3 or 4 opponents, maybe even the entire team, alone. That is what you want. You are a wall designed to cover the towers.

Even when you die while Revive or Teleport is down, you have (-Time Dead) runes and masteries, combined with Karthus' Passive, makes 8 seconds reduced for the undead time, then 20% + 15% (runes) + 10% (Masteries) that will effectively make your time dead at level 18 about 28 seconds. Yes, it will seem like you're always alive. Yes, you will be extremely annoying, and this is while even your Revive is down.

Q - Lay Waste:

This is your harass move, long range and damage. You will learn how people move and will be able to lead them to land the hits. Remember to use this while enemies are still in range of you (if you're dead), for about 4 seconds before using your ult. That is about 3 shots depending how quick you are with reaction to death.

W - Wall of Pain:

Once someone crosses the threshold of the turrets range, lay this wall behind them, making sure they have committed. This usually will scare people from crossing (even if the odds are in their favor) and making the crosser refuse to go back, forcing him to commit and most likely die, even if he gets the kill on you. This can be countered with blinks, so be wary.

E - Defile:

Have this on for any sort of attack made upon you, the timing of it is pertinent, and will crush anyone in your range. It is basically a slightly weaker version of Fiddlestick's ultimate, but you can toggle it with a high mana cost.

R - Requiem:

This is for snatching kills on escapees, you need to be wary of the map for kills with this. It is probably the most hated ultimate in the game, and for good reason. You don't even need to leave the safety of your base and you can get kills with a well-timed Requiem.

I chose the utility line instead of the offense line because the offense line mostly gives melee stats. You basically have to go through 10 points just get to the final 5% damage reward at the end, that being the only thing benefiting Karthus. The defense line would be a viable idea, going 0/21/9, but I like having all of the utility.

It is up to you, but this build does not require boots. You will not need to run from enemies, or chase enemies down. They will come to you if they want to go further, and you have Teleport to move from tower to tower. Lich Bane will provide some extra speed, along with the speed boost from your masteries. Boots are not needed unless you want to contribute in ganking. This build is strictly defending, and covering your towers.

I choose Lich Bane over boots, because it provides speed alone with other benefits to your offense/defense. As well, Lich Bane can be subbed for Warmog's or another RoA, if you prefer being extra tanky at the expense of some damage/speed.

Guardian Angel just enforces the annoyance that this build is, even if the opponents manage to kill you, you will just respawn, while under a turret, which should be providing more damage while they wait for you to pop back up.

The entire builds defense and magic resistance combined with having 2.5k HP is quite survivable, especially for a mage, who is basically always alive anyways. You will be able to defend amazingly, even with a poor team, with this build.

I choose Revive and Teleport, to be used as a combination if you die, or Teleport alone if you notice a tower is not being guarded... or a teamie needs help defending a tower.

You could sub out Revive for Fortify, if you want to be less of a harasser, and more strict on tower defense. I like the general idea of Revive with this build, as basically Karthus will always be alive, the enemy will have to break through 3 walls just to finally kill you. They need to break your Guardian Angel, then Revive, then kill you with both of those timers down. And even then, you will still be attacking for 8 seconds, uninhibited, 2 times. You are sure to demolish anyone who wants that tower you were guarding.

Pros:

- Extremely tough for a mage (Offtank-like stats)
- Always seems to be alive
- High damage potential
- Decent harasser
- Of course, huge global damage

Cons:

- Slow movement speed
- Can only guard 1 tower at a time (unless you choose fortify)
- Can't leave the safety of the tower or team (because of a lack of escape spells)


The great thing about this build is, even if you decide to go into a team fight, where Karthus is usually main-target, you will be extremely durable and long lasting, while still dishing out tons of damage. Just make sure you aren't dragging behind your team to get ganked from behind alone.