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 is a basic build that i use for an AP Katarina build.
Basically what this build is to do is increase the awareness of how an AP Katarina works and good it actually is.(if used correctly)
With this build i've been able to get many triple kills with ease, of course since triple kills are easy double kills are just as easy heh.
here is a quick video of the slight power of an AP Kat, this is kind of an old video but its still a good learning tool :D