Looking to replicate this sludgy insanity.

down tuning the bass is the key more than the pedal I think.

 

This is one of the best "How'd they get this sound" clips I've heard. That tone is gnarly! I haven't posted anything in effects in nearly a year, and that tone clip snapped me right back into it.

I tune to E0 (20.5 Hz) and I've noticed that having a string that has the proper tension is key to getting a proper translation for not only your pickups, but your effects and amp as well. The only company I know that make a string big enough is Kalium Strings. I use a .222, but they make them as big as .266, big enough for A-1 (13 Hz!)

But back on the tone, it's so hard to tell I think with sounds like you posted because they are obviously stacking some dist/OD/fuzz to get that. Pedal order obviously matters, but I'll do my best to give my two cents.

First off, stacking just about any distortion or fuzz with a Darkglass B7k or B3k helps give that Titan-rolling-car sized-boulders-in a-volcano sound. I've really enjoyed putting my Earthbound Audio Beast (muff circuit) and Iron Pig (Rat circuit) in front of the my B7k, with the settings being very mild on the B7k, almost barely overdriven and a bit of treble added in with nothing else on. Then spiking some eccentric settings on either (or your muff or rat variant of choice) in front of it gave me some tones equivalent to a centaur gargling shards of glass and agony.

Another wild setting that works for me is using another OD AFTER the B7k. For this, I've had success with Brinstone Audio's XD-2 , Okko's Basstard, and VFE's Pale Horse, but they responded differently with the amount of gain the B7k was putting out. The XD-2 really sounds more like an overdrive to me personally, rather than a distortion. Because of that though, it handles just about anything in front of it very well, but is also incredibly responsive which tells me that just about everyone that's ever used one has gotten something different out of it than somebody else. Your bass, pickups, active/passive, boosts, EQs, and compressors all seem to play a role with the XD-2 than most pedals I've tried, it doesn't have an imposing "Brimstone tone" like some pedals like Darkglass. Also, the Pale Horse is probably the best tube screamer circuit I have ever tried. It gives an insane amount of sizzle on both bass and guitar, and is very adjustable.

Again, stack order and any other variables in your chain that are seemingly insignificant all play a role. But I want you to get that tone, we need more bass tones like that in the world. Stack 7 distortion pedals if you have to, I can only give you help with the pedals I've tried in obtaining my own doom tone.

 

This sound reminds me of the time I used a whammy to down tune one octave lower on the bass and into a hoof fuzz as distorsion. It worked quite well for this type of doom/sludge sound.
A muff type fuzz or a distortion designed for bass should do the trick but I can't tell which one for sure.

 

Awesome tone and awesome song

 

Killer sound...I would guess a metal distortion through a tube amp just might do the trick. try the egnator black metal distortion or perhaps the amp tweaker fat metal.

Egnator black metal


Amp tweaker fat metal

 

Don't love the music, but ya gotta love that sound . Dang!!!!!