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.
First look, pretty standard AD Katarina Build, but with one gimmick different - Randuin's Omen: hence Omenrina. For a long time, AD Katarina was consider inferior by many AP Katarina critiques that it lacks slow, and relies on Exhaust.
And it has just been last couple days, that people start realizing that Randuin's Omen is a perfect item for AD Katarina that strengthens her in the area that AP Katarina excels in: Survivability and Slow. With a 60 second CD on Randuin's AREA OF EFFECT slow, you will have a deadly AD Katarina Build that's a tough nut to crack.
As for those claiming this build too "expensive," AD Katarina perhaps is one of the best farmer in game. Most of the game will end after your Omen or after your 3rd BF.
Haunting Guise is a debatable item, but I personally like its magic penetration and health for cheap. The little AP to up your Shunpo isn't that bad either. If you don't like it, you can opt to upgrade your BF Sword to Bloodthirst earlier.
Many claim you don't ATTACK on AD Katarina and that Infinity Edge is useless, but LOOK at the monstrous base attack the item offers. And a lucky crit with your 500ish attack with IE is NO SMALL hurt.