if you are against a mage mid it can be tough at times to cs, just try your best by using your Q and getting close enough for a W. Use shun po to escape ganks, dodge skill shots, and to make yourself look pretty dang fancy while CSing. Your combo for harass is Q-E-W then run away while your speed boost from your W is on you. I really try to avoid doing this until I have got my Haunting Guise. Once you get your ult kat becomes very, very scary. You can use this in addition to your Q-E-W combo because it has such a low cd or use it to go balls deep and get a kill. A couple Q's and a combo+ult with a well timed ignite is almost always an easy kill while laning. I won't talk much (if at all) about post lane phase because it is basically the same for every Kat guide. You just have quite a bit more health now.

So, as stated above this is a brief guide. I can't play the game for you guys so you will have to be the ones to test and hopefully succeed with this. Basically the reason there isn't many AP items in this build is because of the scaling on Kat's abilities. Every single one of them excluding her ult basically doesn't scale with AP very much. Her ult scales so high that you don't actually need that much AP for it to be effective. For this very reason MP is the best route to go. And what good is a Kat if all she can do is get half an ult off and die? That is the reason the tanky items work so well with her. You are actually durable enough to finish that ult, do a couple combos, and ult again. (if there are any enemies left, but considering you probably just got a penta that won't happen. Anyways the items are explained above and they are pretty much universal. By that I mean the build itself shouldn't need to be altered, it works against everything (except for those extremely fed Yi's, but no one plays him as an ADC so you are golden) I've had pretty much nothing but success with this build so have fun! Feel free to leave any questions or comments and I might read them.

Flash- Yea this is a must, I shouldn't have to explain why.
Ignite- another must! Idc if your ult has the same healing reduction effect, the fact that you can use it on someone DURING YOUR ULT is enough to make it a must. This increases your kill potential a ton.