Katarina has always been the champ with two abilities and one item: gunblade-flash-ult. period. her little dagger thing is useless if she doesnt hit you, and if you time it right it, just poke her when she tries to get it, she runs away for cooldown. other then that, all she has to do is flash ult a team fight, and she will take out like 3 people. she is like a world of warcraft hunter from burning crusade into wrath of the lich king: faceroll your keyboard, and do nothing.
however, she is also like ahri, yasuo, and zed, dont feed them, and force them to farm. 9 times out of 10 they cant do anything if htey are forced to farm, becasuie they cant snowball. i always tel my lanes look, she has one kill, shes going to roam, so ward up, and fall back. learn to reatreat. if she comes around, back off and ignore her. so what hapens? katarina will go 6/0 with 2 triple kills.