I disagree with a few of these items and your masteries. But I'm not gonna vote.

this guide obviously works because iv seen him get three pentakills in one game before ~_~

Yep i Agree int he most that Marshmallow26 said, and i agree that Regrowth Pendant is much better then boots and health pots. 1+

you're not very precise when it comes to explaining a lot of things. However, I do get what you mean. Aside from that, i absolutely love your style. I see the effect of rushing a deathcap. Combined with your R skill, each E and Q does so much damage then you just kill them off 1 by 1 slowly doing it after damaging them with your R skill. Loved it after testing it +1 for you

Im glad you offered your opinion. It does help. I'll make sure i update these parts :D
Reason for getting regrowth pendant- regrowth pendant has a very good sell off rate as compared to doran's stuff (blade, ring, shield). you lose only about 107 gold from it. But you get a permanent HP regen throughout the game until you sell it off. 3 pots gives you 600 hp, yes. but the regen from the necklace is constant, and you can regen even when you are about 90% of your hp. you dont need to wait till you're down 200+ hp. I usually dont even use the pot that i get along with the necklace until im ready for a kill. So if we're talking about money efficiency, sell the necklace off and kill 1 or 2 extra minion, you get your boots.
Reason for getting cutlass -> the slow ensures u a 100% kill whenever u do your full combo and ensures that the enemy doesnt escape, provided they dont have flash etc, like i said its alot to do with out thinking the opponent. if you get a revolver first, yes, you might have more survivability, as u can drain a little hp over time, but it doesnt successfully guarantee a kill, if you know what i mean?
As for not getting killer instinct before level 8, i usually mid, and i level fast enough, its more worth it to up ur shuriken first, and if you dont, your shuriken bounces less and has lower damamge. As for picking it over shunpo, its just my preferrance of having that extra few bit of dmg to secure a kill. but it could be situational if you are fighting someone like vlad/swain. Picking ghost is because the extra movespeed lets you get in and out of combat like crazy, further increasing the versatility. my build is more orientated towards mass team fights. which is also why i dont pick ignite even though it gives such a big lane advantage earlier on.

Regarding your masteries, you are right. I like your idea and I have thought bout doing that, but i still wanted max damage i possibly can :D because if you shunpo and ur ulti fails, theres so high probability you'd just die if you dont have flash. Might as well get more damage, hence the do or die thing i quoted above :D but its also based on ppl's own playstyle. This is just an idea. People can copy off it and make their own adjustment.

I'm not a too experienced Katarina player,so I'm not gonna be a smart*** and tell you what to do and what not to,since you're obviously a way better Katarina player.BUT,I CAN tell you how you wrote your guide.And please take this as constructive criticism,not flaming/hating.
Guides should be readable.Avoid abbreviations such as "pot,ulti" which are used in-game to shorten writing.Remember,you're not just writing this for pros,you're writing it for noobs too.Pros don't read guides at Mobafire(or maybe they do o.O),they surely know what to do themselves.And even if this IS a pro guide,which I am assured it isn't completely,there's not reason it shouldn't look pretty.Make it a bit longer,keep updating it,and make it grammatically viable,and I'm sure this will grow into a fine guide.

Not a bad guide for the first read, but then some stuff comes to my mind.
First of all, why get the Regrowth Pendant as a starting item if you don't improve it into something later? It's just a waste of gold, you could just start with Boots of Speed + 3 Health Pots, which gives just as good lane sustainability.
Also, why not get Hextech Revolver instead of Bilgewater Cutlass? It's a lot cheaper, also gives you a healing effect (because of the spell vamp), and can be built into the Hextech Gunblade whenever you want. I don't see a reason for not taking Hextech Rev instead Bilge Cutlass early game.
Not getting a single point in Killer Instincts earlier simply messes up your chances to hit a much bigger hit whenever you're facing two champions (it might happen under lvl 8 even in mid lane). Also, it makes you give up your chance to mess up Vlad's, Swain's, and a lotta champions healing effects. I see no point of not taking it at least level 4.
And I don't understand why you would need to take Ghost with Kat. You're much better off with Exhaust I think, you can just Exhaust your target while ulting him. Because of Shunpo, Kat's chasing capabilities are still awesome.
For the masteries, as you're building into magic damage and magic penetration with all your items, I feel like that the 21 points in the Offense tree (which, as we know, is the weakest of the three) is a huge waste. Why not get 9/21/0 for some hugely increased survivability while still dealing the same magic dmg?
Ok, these are just all my personal opinions, your guide is not bad at all, but I don't really feel that you've justified your points.