1. -I can understand not getting Boots of Swiftness in favor of Sorc shoes, but I just like the added mobility. Saved me countless of times despite Defile slowing. Personal preference I guess.

AAS I feel is nice, but rushing Rylai's tend to net me more kills early/mid game and helps assists in lane with the slow. As I don't build RoA or anything else with health, AAS first item would mean you're an ultra squishy caster. I agree that taking AAS lets you drop Clarity, but oftentimes I find my team lacking a Clarity and getting that point into Insight really assists the team (whereas without it, Clarity gives little mana).

If I were to play more conservatively, I would drop the early Mejai's and build Tear instead, but Requiem is so good for finishing off enemy champions early game, stacks are easy to come by (usually).

As for the Void staff, at that point in the game, if no one is stacking MR, they're wrong. If it happens though, I get a Lichbane. GA is mostly just to protect stacks.

2. I feel MPen quints are underwhelming, the extra AP from quints is also underwhelming. I used to run flat health quints, but I am almost always solo mid, so level 1-3 fights are rare (the time flat health quints are the most useful). Having about 397 movespeed with just Boots 1 is pretty sweet. I'm not too stubborn on this though, I've done AP quints back when I was still an early level 30 summoner. I just stopped using them because they feel underwhelming.

3. That line in particular was meant for ganking, but in teamfights, you want to catch someone who extended too far to poke. Waiting until the fight is over seems... not great. Obviously, if you can land it on their entire team, it is completely worth it.

4. I choose Insight over Greed to be more of a team player. With how well Karthus farms, the extra 180 gold in 30 minutes of time won't make a huge difference. Greed isn't bad, but refilling your whole team's mana in a push I feel is more useful.

Overall, I think AAS is workable into the build, but having blue buff is generally sufficient. Honestly, I don't like to play Karthus because he seems too easy. I've met with success with this build even if my team is incompetent. As I have yet to meet a better Karthus than me in-game (yea that sounds arrogant as hell), I stick with what works.

1, Items: boots of swiftness? u do NOT need these you got ryjais and hopefully a team with abit of cc - the MP is far more usefull, get archangel before ryjais.. archangel is basicly his core item and u wont need clarity so u can get flash, ghost or cleanse since he got no escape mechanism, wont need voidstaff unless they stack magic resist and if u havn't gotten lucky with mejais just forget about guardian angel, you shouldn't die with a archangel

2, runes: mana seals goes better with guardian angel, quints: u do NOT need movement speed enough to get the quints, instead get like magic pen or AP

3, teamfights: "Always start with a Wall of Pain. The slow is ridiculous and lets you easily catch up" they wont run right away, so u wanna save your wall till they are either in a cluster for the reduced armor / magic resist or till the teamfight is over

4, masteries: expanded mind is worth it with mana runes and archangel, replace insight with greed, dont use clarity u wont run OOM with blue buff.

please consider this as constructive critisism. - thumbs up in advantage