OMFG has a total of 9 guns, with 4 of them being available from the start and the other 5 being unlocked at certain floors during your run. Guns are mildly different from each other and almost every gun has the potential to be great with the right prefixes (except for the pistol, which sucks all around).
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[18~24 DMG]
Similar to the pistol both in appearance and damage output, the Peashooter is your starting gun, also being equipped automatically every time your equipped gun runs out of ammo. It has infinite reserve ammo and always has 4 to 5 shots per clip. It can have up to two prefixes and is always of common rarity.
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[18~24 DMG]
Exactly the same as the Peashooter, except that it doesn't have infinite ammo and can have any assortment of prefixes and rarities.
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[72~76 DMG]
A heavy hand cannon that does about triple the amount of damage of the Pistol or the Peashooter, but has a slower rate of fire.
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[18-22 DMG]
An automatic gun with a very high rate of fire, but does low damage and has a very small clip size for an automatic gun.
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[18~22 DMG per Pellet] [6 Pellets per Shell]
Contrary to the previous weapons, the Pump Shotgun only appears after the 3rd Floor, being available throughout the entire run afterwards. As the name implies, you pump the gun to load every shell after firing, and reload every shell individually. It fires 6 pellets per shell, with an average spread between them.
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[23~27 DMG]
Unlocked on the 4th Floor. Slower firing rate that the SMG, but deals more damage and has more ammo overall.
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[9~13 DMG per Pellet] [11~12 Pellets per Shell]
Unlocked on the 5th Floor. An automatic version of the Pump Shotgun, with less damage dealt per pellet and pretty much double the amount of pellets per shot.
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[13~17 DMG]
Unlocked on the 6th Floor. Extremely high rate of fire, low damage and a huge ammo reserve alongside the high ammo clip. Personally I think this gun is the one that better resonates with most good prefixes.
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[14 Pellets per Shell]
Last gun that you unlock, on the 7th Floor. Shoots the most pellets per shell out of all the shotguns, but only has 2 shots before needing to reload.

Weapons in OMFG have rarities! They come as follows:


Guns will have their names and pick-up colors based on their rarity, as well as the rarity included in its name. Common guns have white colored names and pick-ups, and don't actually have "Common" written in the name. Rare guns are blue, Epic guns are purple and Legendary guns are orange.

It's obvious right? The higher the rarity of a weapon, the better it is! Well, yes but actually no.
In OMFG, rarities only determine the chance for a gun to get more and better prefixes. It does not affect the gun's stats at all, only prefixes do that. That means that - even if uncommon - you can find common weapons that are much better than legendary weapons at times! So don't judge a gun by its color and read the prefixes before picking anything off the ground!

Another thing to add: for some reason, whenever you start a new floor, guns with high rarities that you have equipped from the previous floor sometimes go down by one rarity. I don't see any reason for that to happen other than a possible bug.

Prefixes is what I'm calling the effects that any gun you collect can have. Not all prefixes enhance your weapons, sometimes they only have a cosmetic effect or straight up worsen your gun. Not all information in here is correct, since I had to find out about each prefix and their effects by myself, only through gameplay and not rumaging throught the source code or anything like that. All prefixes are listed at random, but I might organize them somehow, eventually.

I don't know whether certain prefixes also unlock after you've gone through enough floors, but my guess is that you can get any prefix starting from Floor 1.

If a gun has the "Standard Issue" prefix, that only means that the gun doesn't have any other prefix, and functions normally without any added effects.

Slightly increases damage per bullet and briefly stuns enemies. Doesn't work on tougher and bigger enemies.

Bullets explode on impact, dealing reduced AoE damage in a small visual sphere around the point of impact. Direct hits do the gun's normal damage to the target, also increased if the gun has other damage increasing prefixes.

Bullets have a yellow aura around them, their speed is slightly reduced and they home towards the nearest enemy.

Bullets deal infested damage. Enemies killed by infested damage spawn a robot spider upon death that will target an enemy to explode.

The gun's rate of fire is increased. That also applies to semi-automatic weapons, decreasing the cooldown between every shot as you click to shoot.

Gun reload speed is increased.

Replaces all bullets with robotic spiders that crawl towards the nearest enemy and explode, dealing increased AoE damage.

Adds a film grain and slight RGB split VFX to your screen if you have a gun with this prefix equiped. Purely aesthetic effect as far as I know.

Bullets have a green aura around them, have their travel speed greatly decreased and their damage increased.

Spread is greatly increased. Doesn't work on shotguns.

Makes the light points in your gun go wild, changing between multiple colors. Also does the same to your damage numbers. Any enemies killed by a gun with "Party-Time" explode into confetti.

Makes the gun pixelated and reduces animation frames, giving it an old-style shooter vibe. Purely cosmetic.

I thought it decreased the gun's general damage, but after multiple tests, that doesn't seem to be the case. I don't know what it does.

All of the reserve clips are placed into the main clip, so all the ammo can be spent without the need to reload.

Increases general damage per bullet by a decent amount.

A red rotating crosshair appears over an enemy closest to your aim (as long as it's in your line of sight), and the bullets automatically fly towards that enemy as you shoot. Pretty much an aimbot.

Bullets deal corrosive damage. Enemies killed by a corrosive bullet will drop a puddle of corrosive acid upon death, damaging any enemies that stand on top of it. It doesn't damage you.

All the map's lights are turned off and instead you have a flashlight lighting directly in front of you at all times.

Only enemies, bullets, crates and explosives are colored, everything else is grayscaled.

Enemies killed by a gun with this prefix provide double the original points.

Guess what? Enemies killed by a gun with this prefix provide triple the original points.

The gun becomes nearly transparent and has a glassy reflection added to it. Purely cosmetic as far as I know.

Increases the amount of ammo your gun has. Doesn't actually increase the size of your main clip.

Gun becomes tiny gun. Nothing more to it.

Gun becomes huge gun. Nothing else.

Bullets deal shock damage. Enemies hit by shock damage start to rotate uncontrolably, being unable to move properly or shoot at you.

Every shot fires two bullets instead of one. Only works on the Revolver and Pistol.

Spread is greatly decreased. Doesn't work on shotguns.

Bullets deal frozen damage to enemies, that freeze them in place for a short while after being hit.

Nope, don't know. I've had comments say that this increases reload time, but I tested it and I see no difference at all on same weapons with and without this.

Shooting the gun pushes you back. If you shoot at the ground with an automatic weapon, it basically makes you fly opposite to where you're shooting.

Replaces all bullets with multiple variations of words that start with the letter "F", used to replace the "Fatal" in "One Million Fatal Guns" and mildly decreases their travel speed. Here's a list of all the words that can appear:

• Flashy
  
• Freaky
  
• Finger
  
• Fast
  
• Fierce
  
• Floppy
  
• Fickle
  
• Fatal
  
• Final
  
• Fragile
  
• Fancy
  
• French
  
• Fake
  
• Festive
  
• Fuchsia
  
• Feeble
  
• Faulty
  
• Flying

Bullets deal flaming damage to enemies, burning them and dealing constant damage for a while per bullet.

No idea man. My current guess is that it can increase the chance for enemies and crates to drop pick-ups when killed by a gun with "Copius", a complete blind guess based on the name.

The gun's shape is turned into a 2D image. Purely cosmetic.

Works like the "Wild-Shot" prefix, but also on automatic weapons, shooting two bullets at the expense of one.

Probably has some sort of similarity to "Copius", however I still haven't found out what either of these prefixes do.

I have no idea.

Spread is almost completely gone, wherever you aim is nearly exactly where the bullet will hit. Doesn't work on shotguns.

The gun becomes golden, all reserve ammo is removed and bullets deal as much damage as any enemy's health, instantly killing them in one shot every time. Shotguns fire a single bullet instead of pellets, I suppose as to not make shotguns too OP with this prefix, though automatic weapons still shoot a damn lot of bullets.

Please let me know if any information is wrong, missing or if I missed any prefix that needs to be added.

In conclusion, this list is not yet complete because I'm a lazy ♥♥♥♥♥♥, but I intend to expand on it and fix everything that needs fixing. I hope you found what you were looking for, and any feedback is highly appreciated.