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 my typical AP Kat build. I chose Heal and Ignite becuase heal comes in handy when you're in death lotus. Other great spells for Kat could be Flash (makes for a great harrass/escape method) or Exhaust if you're a little more aggressive. Majai's is always the first item I get with Kat for obvious reasons. If you find that you're not doing to hot with her, sell the majai's for other useful items accordingly. The Sorc's boots would also be a good choice for this Kat because of the magic pen. This is a guideline really.. Test it out and change it to better suit your playstyle.