[1.3.1] Oro's Sacrifice - Molten Strike # 0 mana cost # Double curse # 225%+ life # 100k+ DPS

Pretty obvious one but still - try to get one with as much added fire damage as possible. Attack speed is also nice as it not only increases your DPS, but increases the life leech rate so to speak.

The perfect fit for this build. Great boost to both defensive and offensive stats. Other options include Belly of the Beast or just a decently rolled rare chest with armor and/or evasion.

No surprise here as well - Doryani fits perfectly with the pure fire damage output. The main reason for wearing it however is the 1% fire leach which is necessary for running Curse immune maps or going full offence with your curse setup. A big point can be made about wearing a high life+resists belt, but that requires either implementing a LS/LGoH as a support gem or running Warlord's mark for the life steal. Further testing will be made.

Even though the passive tree allows for investing in Whispers of Doom as our 2nd curse enabler (4 points away), I feel that these boots "fit better".

The only downside to this helm is completely negated by the fact that we deal only fire damage. The attack speed as discussed is a great DPS and life steal boost and the movement speed bonus fills the gap left by using Windscream boots.

Alpha's howl is a great helm to use for leveling as it allows you to run all of your auras early.

Since we are wearing so many uniques it stands to reason to fill our resists from somewhere and the gloves are the place to start. Try to get ones with Attack speed + 2 high resists (suffixes) and a good life roll. Another thing to note is their base should be armor or armor/evasion - it helps a LOT when it comes to socket colors. Case in point - it took me 520 Chromatics to craft mine...

This is where we get our mana cost to 0. With 3x(-8) we get a 24 flat mana cost reduction which is applied AFTER all the % mana cost reduction nodes from tree/gems. It is also where most of your crafting mats are gonna be invested - get a jewel with Elreon's mod on, use orb of augmentation, regal orb it (if good) and then add something of choice with the blessing font. If you have a lvl 8 Elreon you can add 2 mods of choice. Or you can Exalt your way to perfection.
The amount of flat reduction you need depends on your support gem setup and will be discussed in the Gems/links part of this guide.

Anger + Purity of Fire + Grace/Haste + reduced mana
Anger further adds to the fire damage pool.
PoF not only helps with "elemental reflect" packs but more importantly gives you a ton of fire resist - something we desperately need wielding a 2H and a bunch of uniques.
Grace's added evasion is transformed into armor thanks to the Iron Reflexes keystone. With it you end up at about 10k armor which is just a bit under the 50% reduction. If you're feeling particularly suicidal you can swap it for Haste but even with our CWDT+IC setup I wouldn't recommend it.

A very important thing to note is that with 14% passive reduction from tree you require a lvl 19 reduced mana gem to run all your auras. As discussed in the gear section of the guide you can wear an Alpha's howl helm for the extra 8% reduction and therefore run all of your auras much earlier while leveling.

CWDT (lvl1) + Enduring Cry (lvl5) + Immortal Call (lvl3) + Increased duration (lvl20)
Your basic setup for avoiding physical damage. A thing to note is that it gets even better if you run Warlord's mark as one of your curses. The gem levels can be tweaked to your preference, but keep in mind the requirements for supported levels on your CWDT.

Leap Slam (lvl1) + Curse on hit (lvl20) + Flammability (lvl20) + Curse of your choice
This setup essentially combines your movement skill with instant double curse on all mobs you land on and it costs you 0 mana. This is a tremendous clear speed boost as we don't have to stop and curse each pack twice before going in - we just jump right into them and start chugging molten balls. It also benefits from the increased AOE nodes near the Templar start. If possible you should get increased quality on your Curse on hit gem as well as on your curses.
And when it comes to the second curse we have a lot of choices with our limiting factor being only their Int requirements:
Warlord's mark - My current curse of choice. Main source of life steal that's greatly boosting our Vaal pact. Endurance charges benefit our CWDT+IC. Allows you to switch Doryani's belt for a high life one - just be careful with curse immune packs.
Temporal chains - Not a bad choice as most mobs don't even get to hit you before they die. There's a "hidden" damage boost when combined with burning based builds as it extends the duration of the ignite.
Enfeeble - The best in defensive curses. The only downside to it is the 151 INT requirement at lvl 20.
Elemental weakness - Combine this with flammability and you reach the max possible damage output of this build. Again the downside is the 151 INT reqs but it opens up the door for you to elemental based parties. Another thing to note is that I haven't really tested if the 1% life leach from the belt is enough for a decent sustain, especially with Vaal pact (my guess is no). Finally - getting RBBB on any piece of your gear is going to be tough, unless you go with hybrid armor/evasion+ES gloves.

I'm not sure how to properly write this paragraph as balancing DPS/sustain/mana cost/curses/passives is difficult to breakdown, but I'll give it my best. Please view my current setup as just an example that works (for now) and that I'm open to (constructive) criticism.

Molten strike (lvl1)
The cornerstone of this build is the fact that we don't benefit from leveling up molten strike. At lvl 1 the mana cost is just 6 per cast which is insanely low. With Oro's the conversion plays no part - all of the damage is fire anyway. Both the initial hit and the projectiles benefit from +% fire damage nodes. We also get +0.75% increased fire damage per 1% quality so it's a good thing to have.
Concentrated effect (+20% quality) (160% multiplier)
The biggest damage increase we can get from a support gem. Because molten strike's projectiles benefit from the Point blank keystone and Conc. effect reduces your AOE by 30% it actually further increases your damage. Here's a link to the reddit thread about it:

That being said I find that -30% is too big of a hit to your clear speed and that's why I picked up all 3 AOE nodes near the Templar start, ending up at -10%.
The real reason we run this gem however is for the quality bonus -0.75% mana cost per 1 point of quality. At +20% it's a 15% mana cost reduction which is how we get to 0 mana basically. You'll find more on the math at the bottom.
Elemental proliferation (140% multiplier)
In two words - trash clearer. With Oro's +20% chance to ignite and Culling strike against burning enemies it becomes an amazing support gem. Quality increases the burn duration - nice to have but not really necessary.
Fire penetration (140% multiplier)
Damage increase/resists debuff. Quality gives +0.5% fire damage per point - nice to have but not really necessary.
Weapon elemental damage (150% multiplier)
Damage increase. Quality gives +0.5% elemental damage per point - nice to have but not really necessary.
Faster attacks (115% multiplier)
I've mentioned the importance of attack speed twice now. What I want to discuss here is the inevitable "OMG NO MULTISTRIKE!!??". The problem with multistrike is mainly the multiplier of 180%. This makes it very hard to balance with other support gems. We also have no use for the Increased melee physical damage portion of it - just the attack speed. And yet it still outdamages Faster attacks, but in the case of this build you just can't get to 0 mana cost efficiently with it. If possible you should get quality on your FA as it can get you +10% more total.

Notable gems:
Life steal (130% multiplier)
Life gain on hit (140% multiplier)

So here's the math - you take your base cost (6 in this case) and multiply it by every number after the support gem:
6*1.6*1.4*1.4*1.5*1.15=32.4576
Then you take into account all the passive % mana cost reduction - in this case we have 19% from tree and another 15% from the quality of the Concentrated effect gem:
32.4576*(1-(0.19+0.15))=23.41
AND THEN you subtract the flat mana cost reduction from Elreon's jewelry which is 24 total and that's how we get 0 mana per cast.
There are other possible combinations that work and I haven't gotten to test them all yet but the main thing to consider is having LS/LGoH in there somehow. Also multistrike if possible. And don't forget that just for a few points we can get another 12% mana cost reduction (near the Templar start) and potentially get to run a 42 mana skill for free.

After lvl80 I started the climb towards the witch area and got a double Int ammy (finally) so I had the 151 Int needed for Elem. weakness. When you have that the setup switch is very simple - just replace Fire penetration with Life steal and for your curses you use Elem. weakness + Flammability. This accomplishes a couple of things:
1. Sustain is no longer an issue;
2. You can replace Doryani's belt with a high life one;
3. Curse immune maps are just a time issue as you all you lose is DPS, not your leech;
4. Life leech's multi is 130% (fire pen is 140%) and so the total mana cost of MS drops to ~20. This opens up crafting possibilities when it comes to your Elreon jewels, as you no longer need perfect -8 rolls on everything.
5.Overall Elem. weakness is not only a damage boost compared to Fire pen, but as I said before it opens up party play for the build.