Simply put, read the title.

In all seriousness the only difference in items is going to be whether you go duskblade or trinity force first. It goes like this; if you're fed go for duskblade, if behind go for triforce first. ALWAYS rush RFC after you get full jg item/first tier boots.

Marks: The reason I go 9 AD marks is because it gives you a harder first aa after your Q, since you're primarily going to be ganking/invading more then you'll be clearing your jg camps you need this.

Seals: I went with the flat HP yellows because it makes you a lot more tanky early game. The whole point of this build is to snowball. Simply put, this will give you a stronger invade at lv. 3 and better early game ganks.

Glyphs: I went with scaling cdr blues so that late game you'll have that 40% cdr that you need so that you can get in, and get out even faster. The 3 MR blues are because it's good to have some defense, but past ten% cdr is excessive as you can only have 40% cdr with full build anyway.

Quintessence: I went with the AD quints for the same reason that I went with the AD reds. The reason I went with the lifesteal is just so that you have some better sustain in jg.

The masteries are a big part of the one shot concept with this build.

Ferocity: I went with dmg rather then Atk spd so that your abilities/aa's would hit harder. You won't need the atk spd as much when ganking anyway. Double Edged Sword give you more dmg. Natural talent, more dmg, and bounty hunter for snowballing.

Cunning: I went wanderer so that you can move faster to react to pepole needing helps and faster moving through the map so that you can have a larger impact. Assasin, obviously so that you can pick off the stray targets. Merciless is going to make your Duskblade, and Two-Shiv poison hit a lot harder on your carries, also it's just more dmg. Precision is just so that you'll get some arm/magic pen, the magic pen is for your ult/shiv. Anddd the icing on the cake will be thunderlords. So if they manage to survive the Q+aa, and shiv, the smite will proc thunderlords and pretty much guarentee the kill on them.

Always start by placing 2 boxes at the first camp you'll take. Before the first camp spawns place another 2 boxes at the camp you'll go to next. Take the first camp without smiting, but smite the second one, unless you start on blue side. then take once more camp to get lv 3, and rush the enemies buff that's still left to try and pick up an early kill.

You're always going to want to smite the raptors to clear wards/know where they are. The more invisible/stealthy you are, the better.

Only go for this build when you're ahead in ranked.

+The perk is with this build, the enemy teams carries will have no chance of surviving with this build if played correctly.
+It's a very very very fun build to play when achieved.
+There isn't really much counter play to this build because of how hard your first Q, aa, E, smite hits. Especially since dusk blade can't be removed with QSS.

-If you get cc'd, caught, or even touched really you're dead. You're VERY VERY squishy.
-Your split push isn't very strong compared to other builds.
-vulnerable to oracles lens/pink wards. Which is pretty much the only counter play.

Champions. Just kidding, but to achieve full build you will have to be snowballing pretty hard, and taking kills/cs anytime and from anyone you can.