Level 80 Hybrid Flameblast Elementalist^3.21

Notes

A high risk, high reward build; but this setup minimises it as much as possible due to +125% Cast Speed.

Normally, it takes around 2 seconds to build up 10 stage Flameblast; however with this setup it takes 0.88 seconds or less with good gear. 
Even a single-click flameblast will probably have like 3-4 stages. 

Of course, Flameblast is level 28, so is Mid Act III (Gravicus) which is a while, of course. 
Ideally, you want Vaal Flameblast so you can also trigger occasion implosions, so your first Chaos Orb should be used to buy as high a
quality one as you can from the market.

In the meantime, Incinerate will also benefit directly from cast speed (from Merveil). When I played, I also used Volley on Fireball for initial longrange. 

Golems are also not available until early Act IV, so get Fire Shaper on your first Lab.

Fire Shaper is rather important; as this build has very little ability to crit; but Flameblast can pull off some mighty ignites which you want to Proliferate.
ONLY Once you have it should you pick up Elemental Overload Keystone and Fire Mastery (Crits don't ignite, damage vs. Ignited +100%). 
Since we ALWAYS ignite with Fire Shaper, the mastery penalty is nothing, and it's flat increased damage vs. bosses (mobs will explode instantly anyways).

Feel free to tweak things around. Nychta's Lantern and Cyclopean Coil are very good, quite cheap uniques for this build. Xoph's is optional. If you 
want more cast speed and elemental resistances on amulet etc. feel free to drop it.

Follow the drop down trees when levelling; the order is important-- you MUST prioritise Cast Speed and have two notables of it before you get
Flameblast, along with Faster Casting Support. This is the minimum to use it (these alone will roughly increase its cast speed by 80% by
the time you first get it, making it usable). Ignite Prolif is also recommended at all times.

As always with PoE, DO NOT neglect your defences. We want no less than 4500 Life + ES for endgame on top of maxxed resistances and 80% Phys Reduction.
Also get used to saving your own ass with Frostblink. 

After Fire Shaper; Second and Third labs are Liege of the Promordial (second) and Bastion of the Elements (third). BotE is important to take
before mapping as reflected elemental damage will just nuke you otherwise.

If you can find two green sockets on a Armour/ES armour, feel free to switch in Alchemists Mark over Assassin's Mark; but this is
usually very hard to find; even 1 socket is tough (I got lucky on a Regal Crown which has GRRB slots). 

Full links for the golems are also not specifically neccessary; the main important thing is ensuring Stone Golem (Darkness) gets Meat Shield.

Finally, if you're skilled at builds, you can think about alternate cluster setups, but its hard to beat the Witch area of the tree for this build without alot
of optimal (read: Expensive) clusters.