Some men just want to watch the world burn.

Such as myself.

Hi, I'm Zeddy, and I'm going to talk to you about fire without involving maths. If you did want maths involved, I have your fire-related math in this topic.

I thought fire sucked?

If you're riding the bleeding edge of the metagame where you're maxing out every single status for your weapons with trinket slots then, yes, you're going to be able to murder hordes of enemies a bit faster with the more overpowered gear the game has to offer.

If you're lagging, inexperienced, or tackling a particularly tough mission, then I would still recommend fire-based weaponry for you. Fire damage is also not reduced by being poisoned, so outside of fire-based levels, fire offers a stable source of damage you can rely on.

Also, fire-based weapons set things on fire and that is honestly all I could ever ask from a weapon. It makes stuff burn, what else do you want?

So you like guns

I'm going to assume you just started the game, so the suggested loadouts in this guide will be independent, and reliable for most areas and missions of the game. I will not include trinkets or UVs, but I will include sprites and their perks. Your final, first loadout could look something like this:

Magma Driver
Blitz Needle
Swiftstrike Buckler, maybe a defensive shield
One piece of Nameless and Deadshot (Mask of Seerus instead of Deadshot if available.)
Drakon or Maskeraith
Gun CTR perk

Our objective is to maximize ASI, as this will increase our amount of hits per minute with Magma Driver. The more you can hit things, the faster you can set them on fire. For this reason we are prioritizing ASI and CTR over damage for any loadout in this guide. In addition, ASI lets you get out of animations and start moving and dodging faster, and safety is key. We are not glass cannons, we're survivors.

The reason for Blitz Needle is that fiends as a whole are very resistant to fire, and you will have trouble dispatching of them quickly. You can use bursts of Blitz (not necessarily the charge, but go ahead and use that too if you can funnel them into a corridor you can cover up with it) and shield-cancel out of these bursts for safe kiting of fiends. Beasts are also not particularly weak to fire, and will take reduced damage from the elemental shots of your magma.

Gremlins, also resistant to fire, are fairly easy to kite into charges of Blitz Needle.

The one thing you should be mindful of is mecha knights. They're be resistant to your loadout as a whole. If you have a maskeraith, mecha knights is the ideal time to bring out hexing haze. With drakon, you can brush into them with flame shield and dash away from their charges or carefully place firestorm ahead of them. Otherwise, they'll be dead eventually if you just whail at them with Magma Driver. If you're alone, having them shield is no big deal. It's slow, but mechas can't attack you while shielding. If you have party members, either still your shots or find other targets while your party members deal with the mechas uninterrupted by having them shield your shots.

Ash of Agni
Ash of Agni
Volcanic Pepperbox
Swiftstrike Buckler or a defensive shield
Volcanic Demo set (Mask of Seerus if applicable)
Seraphinx or Maskeraith
Gun CTR perk or MSI (bomb CTR if you use Mask of Seerus)

This loadout is fantastic if you usually have a latent connection or usually play with friends on different servers than you. With fiery vaporizer there is no need to aim, time your bombs, or be anywhere close to anything that can damage you. Place a bomb somewhere in the open, retreat from your enemy and your enemy will go and get themselves on fire.

Just spamming AoA is great for general purpose combat, but the Volcanic Pepperbox is what makes this loadout so fantastic in almost any situation. AoA is pretty bad for most bosses, but autoguns are excellent for single target damage. Pepperbox is normal damage, which means you can use it on any boss and, indeed, any target. Take out lumbers, trojans and lichen colonies in a flash. I made an alt once that beat all the rank missions using chaos cloak, cyclops cap, swiftstrike buckler and volcanic pepperbox. He passed Hall of Heroes by strapping on an ancient set back when that was possible. I was solo for nearly all the missions. When I say that this loadout will take you anywhere, you can take it to the bank.

Your biggest hickup will be fiends and gremlins, but it's no big deal. The fire will be less effective against devilites, but they have less health than most enemies in general so it evens out. Now that greavers are elite enemies, you'll barely see them in regular missions, too. Nevertheless, I would bring additional party members for any fiend area you're doing. You can be above-average useful by taking out trojans, though.

For gremlins, just kite them into single file and expedite them with pepperbox charges. Whittle down menders until they pop up their bubble either by AoA or regular pepper shots and unleash your charge on the bubble to take them out.

The sword option for fire is Combuster and there's already a guide for Combuster.