Talk:Kassadin/@comment-1.36.67.1-20120329065817/@comment-88.186.19.90-20120329094800

Farm like you would against another ranged character. Start with boots, get nether blade at level 2 or 3 and from then on, spam Null sphere on him while replenishing your mana with your last-hits. Karthus should push his lane if he is farming with his Q, let him do it, before level 6 kassadin and Karthus are free gank-meat, so the one who is pushed has the advantage. Your first priority should be to not get hit by his spells, your second should be to maintain creep score, and the third to land any spell you can on him. If your jungler comes from a gank, it is preferable to land your silence before Karthus can cast his wall.

At level 3 onwards, every time your E is up, proceed to silence him with Q, place your E and get back behind your minions like a coward; that maneuver should last a grand total of 3 seconds from the moment you start moving to the moment you get back behind your minion line and Karthus should not be able to land a single spell on you (do it if he doesn't have his AoE turned on obviously). If Karthus chases you, remain just oustide his defile area and wait for null sphere cooldown before casting it on him; if he manages to see it coming and places his wall, retreat and try again after the wall has disappeared.

At level 5, stop the harass once he is at half health or less, throw in a few null spheres from time to time to counter his health regent and wait for level 6. Once you reach it, immediately use your standard burst combo (R-Q-E), finish him off with autoattacks and you should net yourself a kill. Good karthus players will know about it and will be weary when you reach level 5; use it to your advantage and zone him.

After that, clear your minion waves as fast and as aggresively as you can, then roam.