[Build] Corrosive FL4K aka "the Green Machine" (WIP)

With this build you can laugh at elemental mulitpliers and can lay waste to mobs with damage numbers as green as FL4K’s eye. The cornerstone of this playstyle is the Flesh Melter artifact type which provides huge corrosive damage boosts provided you’re quick enough to get kills.

This purpose of this build is to use corrosion at endgame. It should be noted that even with maximum Flesh Melter stacks fire and shock will still be better for flesh and shields- is corrosion the most powerful element? Definitely not. Is it the weakest? …Probably. But is it viable? Absolutely.


Note: This build assumes that you have all or most of the Guardian Rewards, particularly Topped Off.

Here’s my current spec; it’s fairly standard for damage and is pretty flexible for swapping between COMs. There’s definitely some things I could change though- in particular, I’m considering taking some points from Hidden Machine and putting them into The Fast and the Furryous.

Below are some explanations for certain skills that this build takes:

  • Fade Away - Because we’re going for damage here. Plus with Topped Off and the Impaler you can achieve some major cooldown reduction which makes Fade Away much more viable for mobbing. For maximum synergy with Topped Off wait for your shield to recharge to full, then take your third shot so that you can end Fade Away with Topped Off active.
    • Not My Circus - For getting enemies off your ass and thus getting more out of Topped Off. Also great with Lick the Wounds in case you get downed during or shortly after Fade Away.
  • Megavore - So that you can deal more damage outside of Fade Away. Also for proccing Leave No Trace and Head Count.
  • Spiderant Countess - The pets’ damage doesn’t really matter but they can gain Flesh Melter stacks and the Countess is the only pet whose damage is entirely corrosive so in the event that she does get a kill you won’t lose the opportunity to get a stack. Plus you can use her action command to teleport her around and quickly establish aggro at a distance. She’s less helpful in boss fights where gaining Flesh Melter stacks isn’t really an option and the teleport isn’t really needed so in those cases the Scorcher works better but against most mobs (including badasses and anointeds) she’s probably the best choice.



Pretty much any high-powered corrosive gun will do but some guns that are either fully or partially corrosive-locked are worth a special mention:

  • Hornet - A Borderlands staple; if you’re thinking of standout corrosive weapons chances are this has already come to mind. This pistol can already rip through most trash mobs and with FL4K’s skills and Flesh Melter stacks it can even take on badasses and anointeds with relative ease.
  • Breath of the Dying - It doesn’t have the same bullet DPS that the Hornet does but the poison nova that it creates on kill is amazing for mobbing and gaining Flesh Melter stacks. If an enemy is close enough to the nova when it starts they can be hit by multiple projectiles; activate the nova right next to them and you can even instakill anointeds.
    • Warning: The nova is very capable of downing you- try not to get hit by the projectiles and especially don’t activate it if you’re by a wall.
  • Hive - Great for deal multiple enemies at a time and getting Flesh Melter stacks in quick succession as well as quickly finishing off anointed militants. Also great with Megavore and proccing Leave No Trace and Head Count.
  • Queen’s Call - Currently the only Jakobs weapon that can come in corrosive. It’s fairly difficult to use for mobbing due to its reliance on crits but Fade Away and Topped Off mitigate that by quite a bit. It’s slower to start than other corrosive weapons I’ve found but once the Overkill damage and the Flesh Melter stacks start working their magic it can really wreck. Against bosses you have far less distractions to worry about while trying to land crits so it’s a lot easier to use there.


  • Impaler - No, I’m not just using this because of the corrosive theme (okay, I initially tried it out because of that but I kept it for the reason that I’m about to explain). This shield works wonders with FL4K for one reason: Topped Off. It recharges to full super fast (by BL3 standards) thus allowing you to gain massive cooldown reduction and use Fade Away much more often. You won’t be able to tank as well as as you would with a Transformer or Re-Charger or whatever but instead you’ll be super mobile and able to play Cunning/B0re Zer0 all over again (minus the kunai of course). (and B0re)

Class Mods

  • Bounty Hunter - Probably the best for general use; the ability to proc Hunter Skills is great for getting Flesh Melter stacks faster. Other COMs can yield more DPS but keeping the stacks going is important especially when you’re initially engaging mobs and when you run into the inevitable anointed.
  • DE4DEYE - Go with this for when you’re sniping and/or using other similarly high base damage guns.

Grenade Mod

  • Ghast Call - This spooky corrosive grenade mod from the Bloody Harvest event already works wonders without a Flesh Melter and with one it’s even better. Great for getting stacks, killing while having stacks and softening up badasses. I recommend throwing them while in Fade Away so that you can have more of them active across the field without having to run through gunfire.


  • Flesh Melter - The thing that makes it all possible. It’s slow to start but keep killing enemies with corrosion and your damage just keeps getting better and better. Any artifact with this prefix will do but the best version of this for FL4K would probably be a Flesh Melter Otto Idol.

Utility gear

  • Non-corrosive weapon - Unfortunately there are some enemies which are immune to corrosion (looking at you, dark corrosive heavies) so this build will need to use other elements to deal with them. I like to use Roisen’s Thorns for this to keep with the corrosive theme.
  • The Transformer - For rocket spamming.

Gear I need to look into

  • Corrosive sniper rifle - Sniping tends to be the best survival strategy a lot of times for FL4K (cough Slaughter Shaft) and I haven’t really found a corrosive sniper that I’m really satisfied with yet. Obviously the Lyuda would be the best choice but I unfortunately haven’t found a corrosive one yet so I’ve been using a Proton Rifle instead.
    • Dear Gearbox: please add more legendary corrosive snipers because right now there are two and only one of them is actually worth using.
  • Elemental Projector - For boss killing since Flesh Melters are mostly only for mobbing.
  • Creeping Death - This gun is currently bugged and can’t inflict DOTs so it’s really weak as a result. I’m still looking out for it in case it does get fixed and/or buffed again because it’s the only corrosive-locked shotgun and it looks ■■■■■■■ cool.


The key to dealing corrosive damage is gaining Flesh Melter stacks, so focus on trash mobs first and then taking out badasses and anointeds. Crowd control weapons are ideal for this- if possible, try and use Breath of the Dying to finish off trash mobs so that you can gain more stacks with the nova and maybe even damage badasses and anointeds along the way.

With the Impaler and Topped Off you’ll be able to use Fade Away often but you’ll also be squishy so you’ll want to use Fade Away and generally move around a lot- grenades and the Hive can help with this so that you can deal damage and maybe even gain stacks while you’re running around.


1 Like

Added a bit on the Queen’s Call; I used to avoid this gun because I was pretty bad with it (and tbh I still am) but now that I can spam Fade Away I’m getting a lot more out of it

Counting it as a partially corrosive-locked gun because it technically is (King’s Call? What’s that?)

So the Ghast Call seems to be a really good grenade choice for this build judging by all the videos I’ve seen of it being able to wreck on FL4K without a Flesh Melter. Not adding it to the original post quite yet though because I still haven’t gotten one to drop (god ■■■■■■■ dammit Haunt/loot ghosts just give me one already)

1 Like

Thanks a lot for your post! I’m trying it out on my first FL4K having played Zane & Amara previously. I’m going to try the frontloader shield + flesh melter deathless since I don’t have all the perfect gear yet. Thanks again! Cheers

Thanks for checking the build out! tbh I’m not sure if using a Deathless on FL4K is the greatest idea considering how squishy and healing-dependent they are but then again I’ve never actually tried it on them so it might actually work out

Yea not a good ideal at all but it’s only temporary until I find a better artifact :slight_smile:

Got a Ghast Call (albeit an exploder one); adding it to the guide

I’ve been using this with the Cosmic Stalker COM with +3 to Big Game and +2 to Interplanetary Stalker, Flesh Melter Victory Rush with +Corrosive damage, Terror generation & +crit while Terrified anointments on Shield and Grenade Mods, and the following Terror anointed guns in Corrosive: Lucian’s Call, MOARR Linoge, Westergun, Stuffed Shredded Lump, Breath of the Dying, Bone Shredder, Cloud Kill.

I would love the flesh melter victory rush, I’m building the same build with corrosive infinity pistiol, it’s awesome but need the melter lol KrippleMan Xbox. Message me if you need anything to help

I like Fl4k. He is good.