[1.2] 30%+ Instant Leech Dual Claw Guide

Pros:
+ nearly unkillable against groups because every hit will leech you from zero to full hp
+ very high survivability against solo bosses, block + resistance aura stackers will be better though
+ basically map mod immune
+ enough dps for soloing (20k+ AoE)
+ not very gear dependent, does not need a 6L or expensive uniques
Cons:
- extremely high bursts of damage or 1 hits will kill you, since you have no block or stacked up max resistances and life isn't the highest (~5k)
- dps in groups is not too high
- leech gets cut a bit in heavily regen lowering maps because you can't use Blood Rage
- things that stop you from leeching are deadly. This includes desync, stun, freeze and things like extrem slows or temp chains. For the first three, there are counters.

Main Spell
We obviously use Dual Strike with Melee Splash as main dps spell.
Dual Strike is supported with Blood Magic, Melee Splash, Multistrike, Melee Physical Damage and Faster Attacks.
For tough bosses without many adds we swap Melee Splash with Life Leech for an additional 9% leech.
6L:
5L:
4L:
For a 5L, skip Faster Attacks, for 4L skip Multistrike. A 6L is definetely not necessary. Attack speed is high enough without Faster Attacks, it's just a ~30% dps boost.
Quality: Melee Splash gives more AoE and Faster Attacks aspd, these are priority. Multistrike and Melee Physical Damage gives something, but that's not noticeable. Blood Magic and Dual Strike doesn't matter at all. Life Leech doesn't matter too, because we have instant leech.

There are no other options, Dual Strike is the only attack that gives you full instant leech with Bloodseeker (if you want to dual wield them, you can use everything, dps will be lackluster than and Dual Strike is the best dual wield attack anyway).

supportive Spells
Blood Rage: this gives you 10% physical leech with quality and frenzy charges. With passives (4.5% life regen) and full Endurance Charges (0.2% regen per Endurance Charge, we get 5 so 1%) you will outregen it. With Vitality (1.65% or more) you dont have to have Endurance Charges up and have some regen left.
Setup: Blood Magic, Increased Duration:
You can skip Blood Magic if you dont have Alpha's Howl and 3 Auras. Quality on Blood Rage is mandatory, Increased Duration is nice and Blood Magic doesn't matter.

Whirling Blades: no need for movement speed.
Setup: Blood Magic, Faster Attacks:
Quality: Whirling Blades and Faster Attacks is nice to have (I don't have it) and Blood Magic doesn't matter. Also keep Whirling Blades on lvl 1 as it's damage is neglectable anyway.

Flicker Strike: This lets you teleport through mobs right to the one you want to hit (rare or unique mob). Also you mostly will be at that mob, so you can leech without getting desynced. That would not necessarily happen if you run through them.
Setup: Blood Magic if you have no mana left, Faster Attacks if you have a 3g1r for Whirling Blades, Flicker Strike, Faster Attacks and Blood Magic:
Quality doesn't matter.

low level Cast when Damage Taken: For auto cursing enemies, keeping Endurance Charges up or whatever you want to link to it.
My Setup: CwDT, Enfeeble, Enduring Cry:
Slotting you curse here has the upside that you will not have high enough int for a high level Enfeeble or Vulnerability.
Quality: Enduring Cry is nice, CwDT and Enfeeble doesn't matter.

Enduring Cry, Immortal Call or other things you find usefull. I only use Enduring Cry and rarely cast it because of no need and the CwDT.
On both of these gems quality is pretty nice to have.

You also might need to have the Life Leech gem somewhere in a socket if it is not in your inventory.

Auras
Your basic auras are the standard Grace + Hatred. If you have an Alpha's Howl, a lvl 20 reduced mana and one reduced mana reserved passive, you can use one additional 40% aura, I am using Vitality normally and Purity of Elements for Elemental Weakness maps.

The only item you need is a Bloodseeker Claw. For everything else you are very flexible. Also we use Iron Reflexes, so you can mix Armour and Evasion as you wish.

Weapons
You want a Bloodseeker Claw in your main hand and any high pDPS claw in your off hand. I only have a 260 pDPS claw which costs a few Exalteds.

Helmet
For my setup, Alpha's Howl is optimal, because it allows me to use an additional Aura, provides Freeze immunity what can save your life against some enemies and gives +2 to aura gems, what boosts your Grace aura quite nicely.

Other possibilites are a Bringer of Rain for a cheap 6L and some block chance or any rare helm with life, resistences and high Armour/Evasion.

Chest
Here a rare Armour/Evasion chest with life and resistences is best. A 6L Lighning Coil would probably be even better if you can make up those resistences
somewhere else.

Gloves
Rare Gloves with life and resistences as always. You can also get flat added physical dmg and attack speed here for a nice dps boost.

Boots
Rare Boots with life and resistences. You don't need movement speed because we use Whirling Blades for movement.

Belt
Again life and resistences. Another good thing is armour and Weapon Elemental Damage would not hurt, but is probably too expensive for it's use.
You want a rustic sash as base item for the % physical dmg.

Amulet and Rings
Attributes to look out for are life, flat phys, int and resistences. Life Leech is also a nice stat you can get.
Note that you need at least 21 int from gear if you take two 30 int nodes and use 95 int claws (Bloodseeker is one of those). You might need more if you have a higher int requirement claw. More doesn't hurt also since you can skip those 30 int nodes then, I have a total of 85 int on gear.

Flasks
I use two instant life flasks with dispels shocked and removes bleeding, a Granite Flask with charge recovery and increased armour and a ruby and topas flask with charge recovery or extra charges and dispels shocked. On the ruby flaks dispels shocked is not needed.

Also switch out the non-life flasks for other Granite/Resistance flasks as you need them to better prepare for map bosses. For huge single elemental bosses like Temple Piety having two flasks of that element is good.

The tree basically evolves around getting the keystones RT, US, IR and the claw leech nodes and most life and damage nodes on the way.

lvl 89 with two Bandits: 107 points tree
basically finished tree for lvl 92 with two Bandits: 110 points tree
(you need to respec a few nodes for that one)
My current tree at level 88 looks like this
I have 30% phy dmg instead of 16% phys and 12% life and will respec that later, it is not a big deal so I haven't done it yet.

You can adapt the tree to your needs by going more offensively, getting some life or more armour. You may also need a bit int to be able to use claws since I have tons of it on my gear.

Leveling Tree (note that I haven't lvled with this build but with a similar CI one and it is over half a year ago, so it is not optimal):
24 points
Starting on the left path and picking up life on the way to Resolute Technique.
41 points
Resolute Technique, life on the way and starting on the right path.
61 points
Iron Reflexes and pathing to the claw leech nodes.
78 points
The path to the claw leech nodes for starting using Bloodseeker.
101 points
Geting some damage and life, Unwavering Stance, the aura nodes.

Normal:
Oak for 40 flat life is best and no one is not too far behind. I currently have none because I started the character planned for CI and haven't respecced.
Cruel:
Oak for 18% physical and Kraityn for 8% attacks speed are both good. With the huge amount of %phys we get, Kraityn might be better. I got Oak here.
Merciless:
Oak for the Endurance Charge or no one. I killed no one because I felt 5 charges are enough, but with 1.2 I lost one charge so I think Oak is the best here now.

My Stats with my lvl 88 character, the tree posted above and Cruel Oak as the only Bandit I did not kill.
Note that these Screenshots are with lvl 16-18 support gems and auras as the support gems recently got switched to 20% and the auras are on another character. So my dps will go up as I lvl the gems again.

Marauder
This build is totally viable as Maurader, you need to take a useless mana node in the duelist start area and a Armour node at the Marauder start. Everything else stays the same.

Ranger
You can also take Ranger, though you loose Armour/Life nodes and gain worse Evasion/Life nodes. This is worse then the other two but still doable.