Endgame made easy + fast: Instant Leech Dualstriker on a decent budget

High enough DPS to clear quickly and beat all of the bosses and endgame content
All map mods except No Leech are OK *Physical reflect mod requires a bit of effort, check FAQ section below
Pretty much never die unless you get oneshot, or make a serious mistake; high life total + mitigation make oneshots rare
No need to curse, juggle equipment, swap gems, use complicated skill rotations, etc
Relatively low cost; you can get running with minor investment, and upgrade as you see fit
Extremely flexible gearing, with only 1 required, 1 recommended, and 1 optional unique
No need for a friggin Watcher's Eye (though you can make use of one)
Pure phys damage (unless you go for an elemental variant) means no need to worry about monster resists, penetration, etc -- it's bankable damage
A crit build (flask charges with Surgeon's) with no need for accuracy rolls on gear
No reliance on regen or flasks for survival!

Melee build. Some people don't like it, and you can't offscreen things
Not the most engaging build. Good for me, as I'm listening to an audiobook and petting my cats with one hand while I play, but not everyone's cup of tea
Not a meta 10 mil DPS build
Movement speed isn't great, and Whirling Blades runs out of mana eventually
No MF (unless, of course, you cut DPS or survivability)

Permanent Fortify
6% less damage taken assuming you've hit something "recently"
You have some options here (see variants below), but with my version of the build, you have:
79% cold and lightning resists
75% fire resist + Arctic Armor (effectively 78.25% fire resist with lvl 21 AA)
not a ton of armor (~3k-6k, depending on gear choices), but Arctic Armor helps
not a significant amount of evasion, but evasion is practically useless for this build
no dodge, but again, it wouldn't really do much anyways
~19% block chance, but it doesn't really make much difference
With my current gear (@ lvl 92), 6541 life; ~8000 expected with a couple of levels and final gear
Regen can sustain Blood Rage with tiny (20-30 life per second) degen, but positive regen if you've taunted recently

~150k dps with no buffs and current gear vs shaper/guardian
~320k dps with power charges, frenzy charges, taunted an enemy recently, enemy is maimed, enemy is taunted vs shaper/guardian
~580k dps with the above + flasks
~1 million DPS with buffs+flasks+my final gearing target -- YMMV
86% chance to hit... until you do, then 100% chance to hit
Mana sustainable via leech
"Free" splash damage from Might and Influence

Chest: Dual Strike-Multistrike-Brutality-Melee Physical Damage-Ruthless-Maim
Helm: CWDT-Blade Vortex-PCoC-Increased Critical Strikes
Gloves: Whirling Blades-Faster Attacks-Abyss Jewel-Abyss Jewel (Lightning Golem-CWDT if you don't have 2-socket Tombfists)
Boots: Enlighten-Purity of Ice-Purity of Lightning-Arctic Armour
Main hand: Ancestral Protector-Blood Rage-Enhance
Off hand: CWDT-Immortal Call-Frenzy

Note: alternate gear choices are below in the 'variants' section

*REQUIRED UNIQUE* Bloodseeker: You want as high of a damage roll as you can afford. Corrupted is OK, but should still have the %life leech implicit.

Rare claw: No shocker here. Some combination of attack speed + flat phys + %inc phys + crit chance + crit multi. You'd have to plug your exact gear/build into PoB to crunch the exact numbers. Really, any implicit is fine; Theoretically, either %life leech for more leech, or life+mana on hit for mana sustain in case of -60% recovery (I've had no problems with it, but I suppose just in case?)

*Optional Unique* Belly of the Beast: Dat sweet, sweet life. There are other options, listed below in variants.

*Recommended Unique* Tombfist (2 abyssal sockets): 1 socket Tombfists probably aren't worth it over good rare gloves; 2 almost certainly are, unless you can afford >10ex gloves with high life, strength, IAS, and flat phys. Even then, they probably won't match its life boost, and life > DPS. However, if you can't afford them (or until you can), rare gloves will do nicely. High life roll is key, but you can either boost DPS with IAS or flat phys, or cover resists until you can get better gear in other slots.

Rare boots: Life, movement speed, and a ton of resists. You might think that movement speed isn't very important since we mostly use Whirling Blades to move around the map, but movement speed is very important since claws have very short range, and we have to move around a few steps constantly in fights. Bonus if you can get a good enchantment, the best of which is probably attack/cast speed if you've killed recently, however it isn't required, and Two-Toned boots would definitely be a better ROI.

Rare helmet: The freest slot of all. Life + resists. Again, a good lab enchant is nice, but it's really just icing on the cake.

Rare belt: Rare Stygian Vise. If we didn't have to think about resists, then Darkness Enthroned might have a shot. But we do. So life and resists.

Rare amulet: We're looking for (what a twist!) life, flat phys, and crit (multi and/or chance). Resists as needed.

Rare rings: If you're surprised that we're looking for Steel Rings, then wecome to PoE. Again, life, flat phys, and crit. Resists as needed. One option is to aim for the reduced reflected damage taken Elder mod or Insanity Essence, however it's going to increase the price and reduce the quality of the other mods.

Q: You said that this build can run reflect. How?
A: You have a few options. You get 25% reduced reflect from the Pantheon, and 20% from Fortify + 6% from having taunted an enemy. That's 51% unconditional, plus 13% less from Arctic Armour. You should have ~5% avg leech if you have a 2% leech offhand claw, so since 18% (red map reflect) * .49 * .87 = ~7.7, you have a bit of work to do. Yes, we have almost 20% block, some degree of mitigation from Immortal Call, plus our abysmal evasion, but at 7.7%, you're still in danger of oneshotting yourself, so there's no need to worry about those. Plus, you need to be able to still net positive leech in case you, you know, take damage from something other than yourself.

You have a number of options:
10% reduced from Master of Force on the tree
10% reduced from Elder/Insanity rings
15% less from a basalt flask
40-50% reduced from Determination+Watcher's Eye

But my preferred solution is 40% reduced from Sibyl's Lament, assuming that one ring either doesn't have any resists or you're not running a PRef + EW map.

An additional 10% reduced gives .18*.39*.87=6.1%
An additional 20% reduced gives .18*.29*.87=4.5%
An additional 30% reduced gives .18*.19*.87=3%
An additional 40% reduced gives .18*.09*.87=1.4%
An additional 50% reduced gives 0%
15% less gives .18*.49*.87*.85=6.5%

IMO, 40% is unnoticeable, 30% is safe (enough), 20% is certainly viable, but will reduce survivability due to less leech. 10% is risky. Additional %life leech would improve things at any level.

Q: Why do you take X passive over Y passive?
A: I'm going to assume that you're asking why I don't take a DPS passive over a life passive. It's because the build has enough DPS that marginally more isn't going to make much difference, while marginally more life can keep you alive. If you think that you see a different error, then by all means, point it out in a post.

Q: Why use Dual Strike? It's not very good. [insert skill here (cough cough blade flurry)] is so much better!
A: Dual Strike gives us free (offhand) splash via Might and Influence. It also benefits from a mechanical quirk where both weapons give us Bloodseeker's instant leech, rather than just Bloodseeker, effectively doubling our instant leech. Cleave is the only other similar active skill, but 1) its threshold jewel only gives us fortify, which we already have, and 2) it doesn't work with claws. Also, I hate using meta skills.

(probably) to be continued...

I'm listing these roughly in order of their interest to me, rather than strict viability.

Alternate support gems:


Alternate armors:


Alternate helmets:


Others: