[3.2] Press X To Not Die Marauder (RF)

This build is set up to take advantage of the Juggernaut ascendancy node "Unbreakable". By wielding Essence of Insanity weapons in your main and off-hands, and another set of Essence of Insanity weapons in your weapon swap, you can make it so that you'll take 4200 physical damage every single time you swap weapons by wearing two Heartbound Loops.

The damage dealt by Heartbound loop counts as a hit, so it not only triggers Unbreakable's "1.5% of total physical damage prevented as hits in the past 10 seconds is regenerated as life per second", but also triggers Unflinching's Endurance charge gain on hit and Endurance charge gained per second when hit recently.

This setup enables you to have effectively 100% uptime for CwDT Immortal Call, giving you 100% phys damage reduction, and converting nearly all the damage dealt from weapon swap into regen per second over 10 seconds.

~3600 life regen per second means you probably aren't dying
Effectively 100% Immortal Call uptime, although there's still a slight risk
Basically ignores all lab traps, even moreso than most Juggernauts

Can't use active skills effectively. When you swap weapons, your active skills have a delay before they become usable. This means you need to rely on movement speed, and also means you can't use Scorching Ray.
Can't use any non-CwDT skills in your weapons. This means you can only use those sockets to level gems.
PC only, XBox owners need not apply
Medium-high budget for such an inefficient build. Needs 4 essence of Insanity weapons, and wants an Essence of Horror for the RF 5-link.
Requires you to constantly press your weapon swap button. PoE is now a clicker game.
Easy to kill yourself upon entering a new area if you aren't careful. Make sure your Immortal Call consumed a full 7 Endurance charges before you start weapon-swapping with abandon.

https://pastebin.com/4f1Pm6z8

Level 68
Level 90

Unbreakable and Unflinching are vital for this build to function, and should be your normal and cruel lab ascendancies. After that you should grab Unstoppable and Unyielding for the movement speed and damage + AoE, respectively.

RF - Conc Effect - Ele Focus - Burning Damage
The usual RF bread and butter.
Immortal Call - CwDT - Increased Duration
Vital for the build, without it you'll just wind up killing yourself.
Purity of Fire
Not strictly necessary, but still nice.
Orb of Storms - Increased Critical Strike Chance
As a skill you can place and leave for it to last a while, it's the only skill that you can feasibly use while weaponswapping. This plays dual-purpose to proc both Elemental Equilibrium and Elemental Overload.
CwDT - Frost Bomb - your choice of non-fire spell, must be in both mainhand and weaponswap mainhand, or offhand and weaponswap offhand. This is a bit of added convenience against enemies that have regen, and also a bit of extra damage/another method of triggering EE and EO. You can also do a similar setup in your offhand + swap offhand, although there are few spells that have much use beyond a tiny bit of additional damage.

Key Items

You can make due with 1 essence of insanity in both weapon swaps and either two The Oak or Rise of the Phoenix's, but for the most regen you want 4 essence of insanity weapons.

Useful/Important Items

If you've ever seen an RF build before, you know the drill. Essence of Insanity 5 link is the best you can get in terms of links. Keep in mind you don't want added fire damage to spells on any gear, since it'll completely mess up Elemental Equilibrium.

Aspect of the Spider is a 15% more multiplier to damage you deal, and is worth using in RF. Most of the other affixes on this glove are useless to RF though, you'll want to swap it out for a rare with the beastcraft affix eventually.

Movement Speed is king, since you can't use movement skills. Ele Resists are vital as always.

Chest is the usual RF options. My chest isn't even worth linking right now, my next goal is to upgrade to a Kaom's Heart.