Since this is a complete achievement guide, I've tried to describe it in as much detail as possible. However, just like the usual style of this type of game, most of the fun comes from your own exploration, so I suggest referring to the guide only when necessary, rather than copying it completely (of course, the choice is yours).

Due to space constraints, most weapon achievements are secret.

There are currently no achievements in the DLC.

[1/23] Nailed it! - You found the nailguns.

At the start of the game, you can find the first nailgun by going through the alley behind you.

[2/23] Here's Johnny! - You found the axe.

This should be the first axe.

The Shining, of course.

[3/23] The Forty-Five! - You found the pistol.

Next to where the axe was, there is a hidden stone door, inside which should be the first .45 pistol.

[4/23] Hobo With A Double Barrel Shotgun! - You found the double barrel shotgun.

Just after leaving the place where you got the axe, there's an abandoned bus ahead. There's a hole in the wooden wall to the right of the bus. Go through the hole and you'll find the first double barrel shotgun.

Hobo with a Shotgun is a 2011 exploitation black comedy action film directed by Jason Eisener and written by John Davies. Based on Eisener's fictitious trailer of the same name from Grindhouse (2007), it is the second feature-length adaptation of a fictitious Grindhouse trailer, following Robert Rodriguez's Machete (2010). Of course, here is a double barrel shotgun.

[5/23] Pipework! - You found the SMG.

After exiting the maze, turn right, step on the steel coil to cross the wall, and there is a passage in the opposite wall leading to the stone building. That should be the first SMG in there.

Chapter 2

[6/23] It Just Works! - You found the assault rifle.

First, get the "Silver Key", then head to the location where you found DOSMan-2. There is a stone door there. Enter it to find an assault rifle and a large amount of supplies.

Chapter 3

[7/23] Cart Wrecked! - Kill the shopping cart boss!

Story related, cannot be missed.

Chapter 5

[8/23] Extra Crispy! - Kill the flamethrower boss.

Story related, cannot be missed.

Chapter 7

[9/23] Overqualified! - You found the experimental super pistol.

Story related, cannot be missed.

[10/23] Deep State Cleanup! - Kill 25 agents.

They will only appear in this chapter. If you kill them all, you won't miss the achievement.

[11/23] Experiment Failed! - Kill 50 sludge spawns.

They will only appear in this chapter. After a certain time, breaking the green glass jar will make them appear.

Chapter 8

[12/23] Didn't Stick the Landing! - Kill final boss.

Story related, cannot be missed.

[13/23] King of the Dump! - Finish game.

Story related, cannot be missed.

[14/23] Still Here? - Stick to the end.

Watch all the slides after killing the final boss and return to the menu to unlock the achievement.

Enemy kill counters carry between playthroughs, so you can kill 20 rats in one playthrough and then 20 in another new game for example. So if you accidentally miss some enemies in the early game, like rats, don't worry, you can start a new game to get them quickly.

[15/23] Please Recycle! - Get supplies from trash 25 times.

[16/23] Minced Meat! - Turn 30 enemies into gibs.

Both axes and shotguns can produce this effect.

[17/23] Waste 'Em All! - Kill 60 bandits!

If you kill them all, you won't miss the achievement.

This seems to refer to an album. Waste 'Em All is the debut studio album by crossover thrash metal band Municipal Waste. Released on January 27, 2003 on the record label "Six Weeks". This album caused the band to receive the attention of Earache Records, which the band signed to in May 2004. The album's name pays homage to Metallica's debut album, Kill 'Em All. Members on this album are Tony Foresta, Ryan Joy, Andy Harris, and Brandon Ferrell.

[18/23] Unhinged! - Kill 10 no-nosed street maniacs.

If you kill them all, you won't miss the achievement.

[19/23] Taking Out the Trash! - Kill 30 trash zombies.

If you kill them all, you won't miss the achievement.

[20/23] Garbage Juice! - Kill 20 Juicy Petes.

If you kill them all, you won't miss the achievement.

The exact meaning is unclear, but Juicy Pete seems to be referring to a composer?

[21/23] Decontaminated! - Kill 50 hazmat soldiers.

If you kill them all, you won't miss the achievement.

[22/23] Pest control! - Kill 40 rats.

They are harder to defeat than most enemies. If you kill them all, you should be able to unlock the achievement in Chapter 3 at the earliest.

[23/23] You Found Me! - Find all DOSMan mascots.

Self-explanatory. There should be 5. For specific locations, please refer to Secrets. (Pigs aren't mascots, but I've listed some anyway.)

Chapter 1

[1/5] DOSMan-1

After getting the "Copper Key", go back and open the locked wooden door. It's inside.

[1/6] Pigs-1

After exiting the maze, turn right, step on the steel coil to cross the wall, and there is a passage in the opposite wall leading to the stone building.

[2/6] Pigs-2

After getting the "Silver Key", return to the maze and open the locked wooden door.

Chapter 2

[2/5] DOSMan-2

Enter Chapter Two, turn right, and there is a hidden path between the two buildings.

[3/6] Pigs-3

Chapter 3

Boss fight, no secrets.

Chapter 4

[3/5] DOSMan-3

After entering the hall where the floor is covered in green waste, turn left and open the hidden door.

[4/6] Pigs-4

After leaving the hall where the floor is covered in green waste, turn right in the first room.

Chapter 5

Boss fight, no secrets.

Chapter 6

[4/5] DOSMan-4

Not far from the start of this level, after passing a large sewage outlet, you arrive at the location shown in the first image. There is a small hole where the arrow points.

[5/6] Pigs-5

Chapter 7

[5/5] DOSMan-5

After entering the room with a bunch of large glass jars, turn right and open the hidden door at the end of the road.

[6/6] Pigs-6

It seems you need to step on the hazmat soldiers in yellow uniforms to get up there. You can't jump up normally.

Chapter 8

Boss fight, no secrets.