DOOM Eternal

If you use either the IDKFA cheat code or the "All cheats" codes before getting this achievement, it may glitch. I recommend not using those codes at all until this unlocks.

There are 9 weapons in Doom Eternal. Two of them--the BFG and Unmakyr--do not have masteries. Of the remaining 7 weapons, the Super Shotgun only has 1 mastery and the rest have 2. This means you have to master 13 weapon mods to unlock this achievement.

To master a weapon, first you must buy its upgrades. This costs 9 Weapon Points per weapon, and if you beat every single encounter, including the surprise encounters, you'll have enough Weapon Points to unlock everything after clearing the second fight in the final level.

In order to master a mod, you have to unlock a weapon through progression, unlock the upgrades for the mod, and then complete a mastery challenge. Some of the mastery challenges are simple and will easily be done through play, such as the ones for the chaingun, while others may prove to be situational and not always register, such as the auto-shotgun.

Fortunately, starting in Mission 10, you will find 7 mastery tokens throughout play. These allow you to unlock mastery in a weapon without grinding through the mastery challenge. Since you could use these for any challenge, it's possible you could waste a token to auto-complete an easy challenge and then waste time grinding on a tedious one. To use a mastery token, select the mod, scroll right, and hold down to purchase.

Based on my playthrough on Medium difficulty, I found these 7 challenges to be easiest. I recommend you unlock any 6 of these you choose these through normal play:

Heavy Cannon: Micro Missiles
Plasma Rifle: Microwave Beam
Rocket Launcher: Lock-On Burst
Super Shotgun: Improvements
Ballista: Destroyer Blade
Chaingun: Mobile Turret & Energy Shield

I recommend you use mastery tokens to auto-complete these and whichever of the previous challenges you haven't finished yet:

Combat Shotgun: Sticky Bombs & Full Auto
Heavy Cannon: Precision Bolt
Plasma Rifle: Heat Blast
Rocket Launcher: Remote Detonate
Ballista: Arbalest

I managed to get this no problem (as I see there are comments about it glitching) so what I did was, I played through the entire campaign and completed it without using cheats, (playing as normal. if you complete gun mastery for certain guns before you reach the end don't worry about it ) I used the gun mastery tokens when i got them on whatever I wanted

then once the game was finished I went back and started farming them here is a list of all required gun mastery challenges. (and levels included on where to farm)

Combat Shotgun - Exultia
- Five Spot: Destroy 25 Arachnatron turrets with a Sticky Bomb
Combat Shotgun - Super Gore Nest
- Salvo Extender: Kill 15 Pinkies with the Full Auto mod
Heavy Cannon - Cultist Base
- Bottomless Missiles: Hit three enemies with a single salvo of missiles, 15 times.
Heavy Cannon - Cultist Base
- Headshot Blast: Get 75 Precision Bolt headshot kills
Plasma Rifle - Cultist Base
- Power Surge: Kill two demons with a single Heat Blast, 30 times.
Plasma Rifle - Cultist Base
- Concussive Blast: Kill at least one demon with the Microwave explosion, 15 times.
Rocket Launcher - Cultist Base
- Explosive Array: Kill 60 enemies while the Proximity Flare is active
Rocket Launcher - Super Gore Nest
- Dual Lock: Kill 15 Prowler demons with the Lock-on burst.
Super Shotgun - Cultist Base
- Flaming Hook: Kill 50 enemies with the super shotgun while grappled onto them.
Ballista - MarsCore
- Instant Salvo: Kill 20 Cacodemons with the Arbalest
Ballista - Cultist Base
- Incremental Blade: Kill at least three enemies with the Destroyer Blade, 15 times.
Chaingun - Cultist Base
- Ultimate Cooling: Kill 5 enemies with a single turret without overheating, ten times.
Chaingun - Cultist Base
- Shield Launch: Deal 20,000 damage while Energy Shield is active.

since it seems people are having issues with the plasma rifle one, i left that till last.

hope it help

Throughout the course of getting all the collectibles there are 7 Mastery Tokens you can get. These allow you to bypass a Mastery challenge and mark it as complete. You can use Mastery Tokens to get this achievement.

Just a few things to know.

1.) You can only use a Mastery Token after you have bought all the upgrades of that Weapon Mod with the required weapon points

2.) You only have 7 Mastery Tokens so only use them on ones you know you find hard to get, Some of the Master Challenges you can easily run out with cheat modes enables which brings me on to point 3

3.) Cheat Mode does not disable getting this achievement. Once you get the Infinite Ammo and Infinite Extra Lives cheat, Put these on when replaying missions as it will make getting master challenges so much easier!

I had the same problem thinking this achievement it's bugged but if you use mastery token you need to complete the challenge mastery for the weapon. In my case I unlocked heavy cannon mastery but in the challenge menu I saw I need the 75 headshots. So I made the headshots and achievement unlock. So like a recommendation don't use tokens for unlock upgrades.