World War Z

MARCH 2020 EDIT: I HAVE NOT PLAYED THE GAME RECENTLY BUT I HEARD THAT THIS HAS BEEN NERFED - USING MUTATORS GIVES YOU ONLY 50% OF REWARDS (CLASS XP, CREDITS AND WEAPONS XP).

As an addition to the detailed guide from JJR0906.

The new patch "Kill It with Fire" released on 29th October introduced the option to select mutators (the ones from Challenge mode) in private lobbies.

As we know the weapon XP comes from killing zombies and the best way to rack up many kills is to use the endless waves - for example the Hell and High Water where you break the door with the train, at the end of the level where you defend the boat, etc. I personally prefer first episode of Moscow - A Sign From Above but I guess this can be applied to any level with endless zombies spawn.

First create a private lobby with bots on that episode. Select Normal difficulty and go to GAME SETTINGS. Select the Mutators option and choose the following:

Cannon Fodder - no special zombies, numerous waves (it's a win-win)
All Flash, No Bang - a lot more weapon spawns. I do no know if there is a set number or it's all RNG but every time I can see between 15-20 spawns if I use a breaching charge and open one additional room.
Thief - 50% more melee damage and because the mutator above has a negative effect - there will be no ammo crates, we use that to regenerate ammo.
Looter - a QOL mutator that regenerates equipment and makes your life easier when you use Medic or Fixer.
Revenge - tipple friendly fire damage. As soon as you level up the weapons kill the bots and let the zombies kill you (or finish the mission if you want)

Optional mutators:

Restless Hordes - zombies will arrive twice as often. I have not used that to be honest and I am not sure if it will be a bit overwhelming.
Die Hard - More health if you need it (you won't :) ).
Crossbow Fiesta and Shotgun Fiesta - guaranteed Crossbow and Shotguns but honestly if you use those mutators don't use Thief and All Flash, No Bang - it's better to use the ammo crates on Easy and Normal that won't deplete.

Use any class you want (if you want to be on the safe side use Medic, Fixer or Slasher). Start the game and play as usual. Not sure if it's guaranteed every time but before you enter the museum check the second big truck on the left side of the entrance (the one that is on the other side of the fence when you start the mission) - there should be a breaching charge. Reach the second lockout (the second area where you are defending). There will be three zombie pyramids (two of them will be active most of the time). Activate the sensor panel to trigger the waves and the defend phase but do not activate any sensors after that. Just focus on defending and killing zombies -they will spawn indefinitely. Whenever you are dry on ammo start killing zombies with melee - there will be some that will climb up to your level. When you have finished leveling up the weapons kill the bots and let the zombies kill you. Rince and repeat :)

Happy grinding everyone :)

Just a small addition to JJR0906 guide; if you have had this achievement glitch (like it did for me) after the first update and could not get it to pop even after purchasing all available weapons.
I can confirm that with the end of August update (proving grounds) and the addition of one new weapon (the classic battle rifle), I was able to unglitch this achievement when I purchased both of the level 5 slots for that new weapon. A friend that also had the glitch was able to pop hers as well, so I would believe that this confirms the method to unglitch this for those who are plagued with an incomplete game. Also note that I left one level 4 weapon unpurchased when it popped

Thanks to PoundofLife89-_- over on PSNProfiles for this inspiration for this guide

1. From the main menu, choose Co-op Campaign
2. Choose Online (Private)
3. Select Episode 3: Moscow, then A Sign from Above
4. Choose Change Class then select Fixer
5. IMPORTANT: Ensure your class is starting with a supply bag, as this will allow you to refill your ammo (for certain weapons at least). I'd suggest the Armory and Knock Knock skill perks.
6. Inside Game Settings, choose Mutators
7. Turn on the following mutators:
   • Restless Horde (fifth 'unique' section),
   • All Flash, No Bang (sixth 'unique' section), and
   • Thief and Looter (both in the common section, about half way down the list of mutators)

You can now select Ready to start playing through the level as usual. Make sure to keep an eye out for weapons around the level as you progress. You won't see weapon crates using the above mutators, but you can press to drop a supply bag and then restock your weapon from that.

At any time, you can press button to check the XP progress of the weapon you have selected - if the XP bar in the bottom right isn't full, you need to fire it at zombies to increase it (special zombies will give you higher XP than ordinary zombies). Unfortunately, the XP required per level seems to vary depending on the weapon.

Once you have maxed out the XP for a particular weapon, find another weapon in the level that you need to progress and use that instead. You can also swap between weapons you have currently on you by pressing .

The mutator options should allow you to find quite a lot of Tier 2 and Tier 3 weapons in the middle section of the level (when you're resetting alarms and fighting waves of zombies). Additionally, if the alarm is ringing and you DON'T continue with using other alarm panels, you should be able to infinitely spawn zombies and gain weapon XP.