Green Tree
Tier 1: 
Grave Sights (5/5)
Since this build loves stackable kill skills and crit damage, this is a perfect pickup for our first skill. With 3 points into 
Grave Power, we'll be getting up to a huge 60% crit damage and 90% gun handling at 6 stacks.
Tier 2: 
Bloodletterr (5/5)
This skill is the crux of this build, and the fact that you can theoretically max it out by level 11 is one of the main reasons that I believe this build is going to be great for leveling. The way that the skill functions exactly still remains to be seen, but going off of the description should be enough information to create an outline spec like we have here. Having a stackable DoT like this is a first for Borderlands, but that's not the only weird part of this skill. As of right now, we have very little clue as to how this skill will scale, which means that a lot of the optimal skill choices for this build are up in the air. But I believe that all of the skills that I chose in this build will directly benefit our Bleed damage, so this is still a safe spec for leveling.
Augment: 
Energy Vampire
The main reason this build uses 
Incarnate is so we can get access to the Energy Vampire augment, which will give us heaps of increases to status effect damage when we get enough kills. Since we are increasing our max stacks for kill skills by 3 with Grave Power, and activating them for free on crit with 
Mortal Terror, we'll theoretically get an almost constant +80% status effect damage, which is a big buff to our Bleeds. The +25% movement speed that base Incarnate gives us should be very nice as well.
Tier 3: Grave Power (3/3)
This skill is a huge boost to the power of all of our stackable kill skills, of which we have 4 very strong skills (Grave Sights, Energy Vampire, 
Grave Assault, and 
Grave Fiends).
Tier 3: 
Target Prescience (2/5)
I really wish we could get more points into this skill, but I think 2 points should be enough. This skill allows us to crit much more reliably with our guns, meaning we get the increases crit damage from Grave Sights, are able to stack Bleed stacks more efficiently, and activate our kill skills more consistently with Mortal Terror.
Middle Branch, Tier 4: 
Drink Full (5/5)
This skill is mainly to help us move down the tree so we can take Mortal Terror, but the fire rate from this skill is nothing to scoff at. You can opt for 
Keen Mind instead if you want to crit more with Incarnate, but keep in mind that we aren't speccing for Incarnate damage here.
Middle Branch, Tier 5: Mortal Terror (5/5)
This is another core skill for this build. Since we're speccing for crit chance on both our guns and our DoTs, we should be proccing our kill skills automatically fairly consistently. Combined with Grave Power, this really pushes how far Vex's kill skills can take us.
Capstone: 
Vibe Check
Honestly, there's not much reason to use this capstone, or either of the other Incarnate capstones on this build. You would be fine leaving your capstone slot empty, but we just take it here so the tree looks nicer and because we're already specced down to it, so why not. It doesn't really impact the build in any positive or negative way, unless there is some class mod that could make use of it.
Blue Tree
Tier 1: 
Sanguine Fiends (2/5)
Spec 2 points in order to move down the tree, and get some nice health regen to boot.
Tier 1: 
Idle Hands (3/3)
We're getting so much fire rate on this build that we're gonna be burning through our mags really quickly. This is the only reload speed we're getting in this build, and it's nice that it's a decent amount of reload speed for just 3 points. It'll let you get that many more bullets down range.
Tier 2: Grave Assault (5/5)
Another one of our stackable kill skills, and this time it's for fire rate. Great for building up as many stacks of Bleed as we can.
Tier 3: Grave Fiends (5/5)
Our last stackable kill skill. 60% global damage at max stacks is just too juicy to pass up. It should be great for increasing both our gun damage and our DoT damage.
Left Branch, tier 4: 
Prismatic Ichor (5/5)
Depending on how this skill works with our Bleed stacks, it has the potential to be VERY strong. If you're familiar with the Contagion skill in Tiny Tina's Wonderlands, this is basically the same thing, but specifically for single target damage. The value this skill holds should really speak for itself.
Left Branch, Tier 5: 
Keen Suffering (4/5)
Giving our DoTs a chance to crit should be a massive DPS boost. If they can benefit from not only the natural crit damage boost but also our Grave Sights skill, then our DoT damage is going to be crazy.
That does it for the max level spec, but what about leveling?
Starting from level 1, here's the order you should spec your points:
Select Incarnate
First five points: Grave Sights
Select Energy Vampire augment
Next five points: Bloodletter
Next three points: Grave Power
Next two points: Target Prescience
Next five points: Drink Full
Next five points: Mortal Terror
Select Vibe Check capstone
Next three points: Idle Hands
Next two points: Sanguine Fiends
Next five points: Grave Assault
Next five points: Grave Fiends
Next five points: Prismatic Ichor
Last four points: Keen Suffering
Vex
Incarnate
