Predecessor Builds > Wraith > Knock Knock % Max HP

Just a concept.
v1.5 Changes: Increased magic scaling on Snipe def helps a build like this. Mana is a bit more of a problem but if you land snipes you can bully them away to make sure you can get river buff.

Mana Potion after Spirit Shiv or at Start.

This build once you get 3-4 items can force people out of fights with a Q > RMB > RMB by pushing them too low to safely engage.

-Infernum and Megacosm help ensure kills on low hp targets by proccing Vanquisher from ticks. Mutilator and Noxia adds a flat bonus to your combo.
Similar Physical Power as other standard builds but, +145 Magic, +5 Phys Pen, +Omnivamp and almost triple the ability haste at the cost of Attack Speed and 80% Crit

-This is a hang back at a safe distance and rely on the damage from snipe + items with your shorter cooldowns. Playing this Mid for the occasional river buff mana regen + Spirit Shiv first back removes the mana concern from no Soul Chalice.

-By the time you have Megacosm your snipe dmg is doing +2.5% max hp + 2.5% max over 3 sec + 5.5% bonus hp over 3 sec + for some reason Infernum procs off of "grenade snipe snipe" (3 hits) instead of 4 for some reason so + ~5.5% of max hp + 10.625% of max hp for first snipe from Q mark (all before armor). Not to mention the second snipe and any of this damage ticking them under 5% procs the vanquisher execute.
Once you get Noxia, add another 6% of max hp to snipe damage combo.

-Guide lists rank 2 Snipe at level 3 first for better poke/clear. If you're not feeling safe you can get E at 3 and rank 2 Snipe at 4.
-Can also max E rank before getting rank 3 R if you need the extra physical pen.
-If they have a lot of healing, you can get Tainted item before Mutilator or Megacosm. Getting Vanq asap is still huge.

Honorable Mentions:
Wraith Leggings: (Fitting I know) 12% Ability Damage to low targets, emphasis on the execution stuff here but probably not worth other max hp procs or the pen/slow of Perforator.
Ashbringer: Good for a bit more auto damage, and solid for reducing cooldowns to keep sniping but goes against what this build is (keeping you far from enemies) by making you go in for autos more.
Soulbearer: Decent for more safety with the shield and magic lifesteal on a combo. Magic damage it gives isnt bad and more mana. Not quite worth the burst of whats listed though imo.
Pacifier: Emphasizes the execute build similar to Wraith Leggings plus a little extra lifesteal and a dash (with cloak jump is nice). Not a bad option.