Starting out with the Doran's Blade can help you get those early on kills.

With the point of the build being to do mass amounts of damage in short periods of time so you can pick people off and get out of range as quickly as possible you need to focus on attack speed next going for the Berserker's Grieves.

The Brutalizer helps add to your damage, but the main point of it is to get that armor penetration and the 10% cooldown reduction.

Follow the Brutalizer up with Phantom Dancer this will help alot with being able to pump out your attacks to stack up the poison counters on your target while also boosting your chance to do critical attacks in the process and the movement speed isnt unapreciated either.

Now that we have our attack at a decent speed we will go for some damage the Black cleaver adds a good chunk of damage along with the -15 armor on hit for 3 stacks can help you deal massive damage to players.

Then you just keep trucking with the armor penetration and damage going with last whisper 40% armor penetration while still adding 40 damage to your attack as well.

At this point depending on your preference you can either upgrade the Brutalizer into Youmuu's Ghostblade or you can go for the Infinity edge. I generally go for Infinity Edge first to add that nice extra 75 damage extra crit chance and that beautifull 250% damage done with crits.

At this point you have the potential to take out groups using your ultimate without even bothering with expunge with how much damage you do (tho its better to play it safe and use expunge after they are low health and run away anyway).

Upsides
Mass Damage, Good Mobility, hero killer, crowd control.

Downfalls
No defensive items so your about as squishy as it gets you have to play more intelligently to succeed.

Success-fullness of hero derived from being able to ambush behind enemy heroes so oracles and wards force you to stay away until your ult is up to pick people off at a range.

Have to be severely careful when fighting someone with a thornmail.

Use ambush to get behind target to where they will try to run past you to get to a safe location in order to give yourself more shots on target without having to move.

While being chased a quick shot then Debilitating Poison can be esential to help you get that needed distance from your attack to go invisible with ambush again.