[3.15] Detailed guide for Explosive Concoction Elementalist

Pros:
-Very simple to play, 1 button to attack, 1 or 2 buttons to move around, 1 to summon totem at bosses, 2 flasks to activate.
-Relatively cheap, 1 ex for barebones, 5ex for decent gear with better dps and defenses. Can work as a starter, I've started with it and never complained that I can't afford the gear upgrades.
-Pretty tanky against large groups of small mobs.

Cons:
-Not the greatest boss killer, especially tanky ones where you run out of charges.
-Targeting can be an issue, you can overshoot mobs and do no damage.
-Small number of available gem slots, if you have any favourite secondary skill setups.

-Flat damage bonuses (like +fire) are pretty bad for this skill, you can ignore them. It's all about +lvl of EC and % damage, secondarily about speed and accuracy.

-The "reduced flask charges used" mod is great, but don't craft it on flasks themselves - it won't do anything. Instead craft some flask generation or extra charges. There aren't any thresholds (like 33,33% and 66,67%) for reduced flask charges used. Any amont of it will help a little by making every Nth cast cost less.

-You want to stay as close to enemy as the safety allows for the Point Blank and Shotgunning bonus.

-Start the boss fight by hitting him few times to make sure the Corrosive Elements are working (25% chance), then go in hard with Cinderswallow flask.

-Extra Area is important, but scales very poorly with EC. You need a significant amount of it for even 1 extra radius. Small stuff like +10% AoE craft on gloves might not do anything, check the PoB first.

-Try to keep up the Fortify from Shield Charge, but don't be to reckless about it against bosses.

-You need at least 24% block chance shield for the full bonus from Glancing Blows and Command of Steel

-You also need flat 35 strength on gear.

How to improve bossing?
- The Berek's Respite ring does almost nothing vs bosses, so before the boss room swap it for The Taming or some rare life / ele damage ring. The biggest damage boost would come from Malachai Artifice with socketed Ice/Lightning golem, but you would have to rebalance your resists for that. Also if you go with Malachai, make sure you don't have any +fire minion damage.

-Get the +charges harvest craft on your ruby/topaz/saphire flasks.

-Try swapping Ancestral Protector for Decoy Totem against some bosses.

-You might also try swapping your normal ruby flask for Dying Sun, hopefully with 2 extra projectiles you can melt the boss down before running out of flask charges.

-Finally, you can swap Dash for Vaal Haste.

White A4 Veritania, A4 Baran. They got pretty slow, once I ran out of flasks, but still ok:
https://youtu.be/1g3ufCcXN2k
https://youtu.be/vQhNVjlaQ3w

T15 Villla + big Harbinger in boss room, T16 Underground Sea:
https://youtu.be/YfC6ZF6IVS0
https://youtu.be/ybE1ClxTQgA

Lvl84 Heist, lvl 82 Loogbook with 50% reduced flask charges gained:
https://youtu.be/H5T3sk7oJDk
https://youtu.be/S3K2hcH9cj4

And here's A5 Sirius, where things are getting ugly and I die many times. I fought him like once in the past, then I had a break from PoE. First I died few times cause I forgot what does he even do. And later I just couldn't see him through all the clones and red on red effects. It took all the portals, but eventually I beat him.
https://youtu.be/a2o9XrFknEA

Few examples of other content I did (not deathless tho) are: Purifier with nasty damage mods; Minotaur with extra AoE and taknyness; Phoenix with Maven constantly healing him (I didn't bring Frost Bomb with me, so it took forever but eventually he died).

I manually added Wave of Conviction for the exposure bonuses, because PoB doesn't recognize Corrosive Elements cluster node. And "15% more damage on belt" to kinda simulate the Cruelty bonus, PoB doesn't recognize that either.
https://pastebin.com/mV1i64HW

Tree in browser:
https://www.pathofexile.com/fullscreen-passive-skill-tree/3.15.3/AAAABQMCdwQHBLMFtQj0DlwTNRR1Fm8XpBpsGo0bNxutG8gfAh9BH0wi9CP2JKonLzB8MPgxwjY9NsU26TfUOq062DwFPQ89Xz3iRX5I7kp9TItMs02STc9QQlFHUlNTNVRHVK5VS1XGVkhW-lsmXfJh4mKsZ6BqQ2wLbIxtGW-Ed9d35Xiue2F8u311fdJ_-4Kbg9uHdow2jX2Nv5BVkPqTJ5eVl_SYU5shnaqdrp7EoS-iAKOKpMKmvqcIpzSxs7TFvorAZsCcwuzPg8_d0B_Tftgk2b_fbd-K42rjn-Qi5FXpUO0_7g7vS-987-vxiv66_xwA?accountName=osesek&realm=pc&characterName=VyacheslavaMolotov

I suggest this order
1) Mind Drinker, so mana stops being a problem forever.
2) Elemental Overload, because it's a big damage boost.
3) Travel all the way to Point Blank, because it's another big damage boost.
4) Then go for the Devotion node in the Templar area, because you need some strength to wear Kaom's Heart (you can also take +30str node and later unlearn it).
5) Careful Conservationist and some side life nodes.
6) Somewhere at this point you should gather enough currency to buy Megalomaniac with Corrosive Elements. Which you socket in the Cluster Jewel socket near the Careful Conservationist.
7) Then take 3 normal jewel sockets for Elemental Damage Grand Spectrum.
8) Finally take the remaining life, block and damage nodes.
9) You're now lvl 90 and the tree is almost complete. But if you play carefuly and get 2 more levels, you can take the final jewel socket and buy a Precision/Vitality Watcher's Eye.

Ascedancy: Mastermind of Discord -> Heart of Destruction -> Shaper of Flames -> Bastion of Elements.
Bandits: Kill all.
Ascedancy: Brine King, Gruthkul or Shakari

If you don't know what Path of Building is, google it, download, install, press "import/export" in top left corner, then "import from Pastebin" and paste the link above.

Helmet: Explosive Concoction - Grater Volley - Elemental Damage with attacks - Cruelty
Cruelty's actual damage is kinda impossible to calculate, but judging from the gem description it fits the build very well. PoB says that other gems are better for bosses, but I wouldn't undersetimate DoTs. It's always nice to deal even small, but continuous damage, when you're busy with dodging.
Greater Volley seems to have pretty similar spread to GMP on small distances, while having much lower damage penalty. Some people even go with crazy stuff like both GMP+GV, I'm not sure is it worth it.

Boots: Shield Charge - Faster Attacks - Combustion - Ancestral Protector
Your main movement skill, to apply both -fire resistance and fortify. Ancestral Protector for tons of attack speed. Try to get the "anomalous" version, so you can place it almost instantly. Take a Forfify gem instead of totem, if you can't afford the Fortify boots.

Shield: Precision, Summon Skitterbots, Vitality.
Your auras (plus Aspect of the Spider). Pretty unusual, but typical auras and heralds actually don't help this skill too much. The level of Vitality and Precision depends on your available mana pool. I suggest at least enough Vitality to counter the Blood Rage degen, for the quality of life.

Gloves: CWDT - Steelskin (or Immortal Call), Dash, Blood Rage.
I would suggest to NOT 4-link this, to avoid linking Blood Rage with CWDT. It's not end of the world if you do, but it's better to control BR manually.
Dash is optional, because Shield Charge is clunky on areas with many obstacles. You can take a golem or something instead.
If you really need gems, you can unlink the CWDT and cast Steelkin manualy or tie it to your mouse left click.

Core items:
Just get a normal Frostferno until you can afford either some EC lab enchant or +2 cold/fire/lightning/area/projectile gems. +2 Lightning damage should give you the best damage for the best price.

Dirst cheap armour, so you can throw in some extra currency on exotic craft.

Very helpful ring for clearing, you gonna love it once you see it in action.

The other items
They're few useful exotic mods on those, but first of all you should focus on filling you resists, strength and life with those.

The +block corruption is not needed. You can leave it with basic strength bonus, since you need it anyway. This amulet can be expensive early, so get anything. I would suggest searching the Trade site for some talisman with decent stats and anoitment, because talismans are very cheap.

The only important mod on this is the life recovery on block. The rest depends on your budget. The dirt cheap alternative is Thousand Teeth Teemu with some reflect on the rest of the gear.

You either need Flammability Curse on ring or Elemental Weakness corruption on gloves, whichever is cheaper. Again, the other mods depend on your budget.

Here lies a pretty important mod - reduced flask charges used. I suggest a Stygian Vise, so you can put corrupted blood immunity jewel in this. The jewel's mods aren't that important, since flat damage is crap. Just get +life and whatever.

Just standard gloves, "increased damage while leeching" is proably the best damage mod you can take on those. If your ring doesn't have Flammability mods, you should search for "Elemental Weakness on hit" corrupted gloves.

Boots with Fortify open up a gem slot and those are very precious for us.

How to get Aspect of the Spider.

You need an open Suffix (there's an option for that in trade site search filter) on either your boots, gloves, belt or a ring. If you've found one of those with the Aspect already crafted that fits you - then take it. But you probably won't.
If you didn't catch it yourself, you have to buy the Fenumal Hybrid Arachnid (~35c), add to your beast book and do the ritual. It will open the fight to the Fenumus portal where you fight the spider. It will probably kill you with poison, but you have 6 portals so that's ok.
But here comes the hard part. To craft the aspect on your desired item, you have to fight Fenumus again, at the Blood Altar. This time you have to kill him before he kills you. It will work even if the poison kills you afterwards. It might take few tries, each requires buying another Fenumus, First of the Night. It might get costly, so leave it until the later parts of the game if you're unsure about your power.


Get the bleed mod until you buy Corrupted Blood immunity jewel, then craft the freeze mod instead.

You hava a room for only 1 damage/utility potion, and this worked the best for me. It gives you both offense and defense against large packs. I haven't figured out a nice way to consume corpses, but with the reduced flask charges used it's not too hard to keep it up. Get the one with "Recover (1-3)% of Life when you Kill an Enemy during Flask Effect".

You want charges generation and extra charges on these. The other stuff isn't that important, but you could always get stuff like anti-poison or anti-curse.

https://pathofexile.fandom.com/wiki/Grand_Spectrum_(Viridian_Jewel) You need to socket 3 of those to get the full bonus.

https://pathofexile.fandom.com/wiki/Megalomaniac with https://pathofexile.fandom.com/wiki/Corrosive_Elements There are few other sources of exposure, I think this one is the smoothest. Use Wave of Conviction + Arcanist Brand until you get this.

Vitality/Precision https://pathofexile.fandom.com/wiki/Watcher's_Eye This is just a cherry on top if you leveled to 92 and have some spare currency.

https://pathofexile.fandom.com/wiki/Lycosidae Should make mid-level gearing up easy, because you can forget about accuracy completely.

https://pathofexile.fandom.com/wiki/Arctic_Armour Pretty cool aura, until you get Aspect of the Spider and need Precision because of swapping Lycosidae for something else.

https://pathofexile.fandom.com/wiki/Dyadian_Dawn Belt with nice ignite damage buff.

https://pathofexile.fandom.com/wiki/Wave_of_Conviction + https://pathofexile.fandom.com/wiki/Arcanist_Brand - You can use it until you for exposure, until you get Corrosive Elements.

Also EC isn't the fastest leveling skill, until you get 3 resist flasks and Berek's Respite. But since you're taking very universal damage nodes, you can level up with any weapon and any elemental attack skill.