Not Updated For Current Season
The masteries shown here are not yet updated for the current season, the guide author needs to set up the new masteries. As such, they will be different than the masteries you see in-game.
This Char was explained in other Builds Better, for example " http://www.mobafire.com/league-of-legends/build/karthus-the-ragequit-master-beginners-advanced-guide-2296 "
Nice lil' trix
1) When kiting a champion, a will timed "Wall of Pain" could eather save ur life or kill ur enemy, EX: when in the forest after u cross a bush place ur "wall of Pain" in the bush, when the enemy walks in there he would be slowed and u can setup "Lay Waste" and do another one he might be forced to run, and might go through the same bush it still might have ur wall so 2 slows, ether assist or a kill.
2) same thing but when walking out of the bush stay close and setup a "lay Waste" after u can "Flash" to the other side, he/she will see no1 in front of him or next to him so he will run back in to the wall again and another "Lay Waste" and maybe a kill!
These are Situational, sometimes flash wont work if ur being chased by more then one soo.... u prob don't want to tele to them, especially if he has a stun XD
This is my 1st build so if there something u think is good or bad about it let me know and Rate it give it a try and leave comments ether about things maybe we can improve or change.
GL and HF, THANX! :D