Theory/Background - (The Why)
Patch 2.6.1 brings 300% to 375% Impale bonus damage to Karlie's Points and raises the 6p bonus of Shadow's Mantle from 40k to 50k. With these 2 buffs, this build should be able to clear approximately 11 tiers higher than prior to this patch. This build is made possible by the Holy Point Shot quiver. With this quiver, impale will throw 3 knives instead of one. Each knife gains the 6p bonus damage from the Shadow Mantle Set. Currently its also possible, if positioned very close to a mob, to land all 3 buffed impales on a single target. So for instance the RG will take 3x the damage from impale than it does w/o the Holy Point Shot if standing very close while attacking it. This will greatly increase the effective damage output for impale. Not only that, all 3 knives will return the amount of hatred that is listed on your Karlei's Point dagger. Now with up to 3x the refunded hatred, it is no longer necessary to have a generator, while staying at near full hatred most of the time. This allows using and taking advantage of the Aquila Cuirass chest in the cube for 2x toughness.
Gearing/Game Play - (The How)
Make sure to have at least 36.7% cdr for permanent Vengeance. The required cdr can be accomplished with cdr rolled on one piece of gear, 15% cdr from the Gogok of Swiftness, a diamond in helm and 10% cdr in paragon. Tactical Advantage passive is desirable to use for speed runs. Use Leech for soloing higher GR's. Numbing Traps can be used to buff group toughness if needed. When pushing high GR's in 4man groups the Single out passive should be used and replace FoK Bladed Armor with Marked for Death (either Contagion or Valley of Death). Nemesis bracers are an excellent alternative to Strongarms and are recommended for speed rifting. For pushing GR's in 4 man's, Lacuni Prowlers can be used for increased attack speed to better stack Stricken. For bounties there is no better choice than the Warzechian Armguards. For pushing high GR's with supports, wear an SOJ and cube the Convention of Elements for more damage, since the with supports the Elusive Ring may not be needed.
The ricochet (lightning) rune of Imaple is best used for lower level content where mobs die quickly such as T13 or speed rifts. The reason for this is that with ricochet there is a chance to have hatred returned on the first cast of impale. The overpenetration (cold) rune for impale is best used for higher level content such as pushing solo GR's when using the Pain Enhancer gem. The reason for this is that overpenetration's piercing impales can apply the PE's bleed to a larger amount of mobs around you. With this increase in the number of bleeding mobs withing 20 yds, your attack speed will be higher. That being said the difference is small. So if you have much better lighting gear than cold, then use ricochet even for pushing solo. In 4man meta group play where the DH is the RG killer, it's less important which rune of impale is used (though all things being equal, cold is better due to the piercing knives' ability to better aggro mobs). Therefore for meta, use the rune of impale that matches the element of the best gear you have.
Try to stack life after kill on chest, belt, pants, jewelry and weapon if possible. Life after kill works beautifully with this build. Shadow Power will add 50% of your life after kill to life on hit, the leech passive adds another 75%. Together you will have 125% of LoK as LoH. This is a huge gain in health recovery, allowing for safe passage while playing very aggressively.
Note that if you play at a game difficulty where you are one shotting mobs, it will result in running out of hatred because there will be no opportunities for hatred refunds from Karlei's Point. Some examples of where you might run into this would be power leveling friends or running fast low level GR's to level gems. In order to mitigate this problem so you don't run out hatred, run Seethe instead of Dark Heart, replace Cull the Weak with Blood Vengeance and replace Aquila Cuirass with Visage of Gunes in the Cube.
Make sure to spam Vengeance, bladed armor and wolf when off cooldown. The constant activation of these skills can be achieved by num locking them. Beyond that, all that is required is to cast impale to attack and vault for mobility. Its really that simple. You do need to make sure to impale every 2 sec in order to have free vaults. I personally use vault actively to stun elites and RG's to interrupt their special attacks. This can be be extremely helpful in surviving nasty fights. Note that while vaulting you enter into a smoke screen like state that renders you invulnerable to incoming damage for the brief time you're traveling from point to point. Make sure to keep the elusive ring buff up at all times. This can be done by vaulting or casting shadow power. If you find yourself placed particularly well, as in next to an elite that you are impaling, casting shadow power to proc the elusive buff is preferable to vaulting if you can face tank well enough to stay in place. Note that this build requires hunting and killing mainly elites, especially for speed runs, but higher GR's will require gathering up and killing large packs of trash also. Just make sure to take advantage of the oculus circles when doing so.
Sand Dwellers (when sanding) and spinning Dervishes will reflect impales which can and will proc/rip not only the DH but the entire party. Please be very careful around these mob types and make sure not to fire into them especially when in a party.
Summary/Wrap Up - (The Results)
The build is very simple to play and a hell of a lot of fun. It gives insane mobility, good damage and high survivability. In fact fully self buffed with all dps gems and nems, its not uncommon to exceed a toughness of 500 mil at low paragon. That's awesome toughness for a dps class with no support. This build can be used to compete for pushing the highest GR's for both solo and group play. For speed farming it is superb. GR 85's are taking under 4 min to clear (with 2 mil+ dps). Normal rifts are fast and fun. Split farming 4man T13 bounties is very efficient. In short the build will do everything you need and want within Diablo 3.
I have thoroughly enjoyed playing and testing out this build and I hope you will find as much enjoyment with it as I have. Please leave a comment below if you have any questions. Please Upvote if you find this guide useful. Thanks.