Borderlands: The Pre-Sequel

I wanted to share my advice for getting the 20 Luneshine weapons from the grinder, without needing any moonstone, if you have a second controller.

With your main character's game running, load up a new character (with a guest account) and drop your level 1 starting weapons. Have your main character pick them up. Do this at least 3 times in a row. Once you have 6 guns (3 of each type), go to the grinder and do a moonstone grind with each group of 3. It will cost you 0 moonstones. Just keep doing this over and over and you will get 20 Luneshine guns pretty quick.

What I personally did was load up a guest account 6 times, dropping 12 guns. That allowed me to do 4 moonstone grinds (again, for free). Repeat. I seemed to average about a 50% success rate in getting a green luneshine weapon. Once I had enough green weapons, I'd also try those too, which sometimes got me yet another (blue) one. It actually goes pretty fast using this method. I got all 20 in less than an hour. Good luck!

The Vast Majority of this solution is a repost of the Xbox 360 Version created by vSully. All credit goes to him for making this guide.
For a handy Xbox One solution, scroll to the bottom of the guide.

This achievement requires completing at least level 1 of each challenge with one character (location-specific challenges are not needed). Many will come through the course of normal play while some will require that you do certain things you may not have done as you played through the game.

If you want to reduce the amount of effort needed, I suggest using each weapon type for at least a little while as you play through the game to work towards many of these challenges.

To view your challenges, press and use to scroll the menu to "Badass Rank."

Not all challenges are available immediately. The following challenges are listed as (undiscovered) initially and only become available after meeting certain requirements in other challenges:

Enemies: The One That Says B.A.M.F.
Vehicle: All are (undiscovered) likely until you get access to a vehicle
Health and Recovery: Soup's Up, Had a Bit of a Shocker, The Phoenix, Rollin' the Ice
Rocket Launcher: Missile Magnet, Punker Buster, Hand of God, Collateral Damage
Sniper Rifle: Critical Reception, Penetrating Wound, Melon Splitter, Ol' Skool
Assault Rifle: Hot Lead Injection, Crouch Potato
Laser: Light 'Em Up
SMG: Dinky Death Dealer
Shotgun: Take It All, Overachiever, Shotty Workmanship
Pistol: Gunslinger, Magnum Maestro
Melee: Captain Cutty

Only two of these challenges took me any effort to "discover" as they required level 5 completion in another challenge: Overachiever became "discovered" after I got 750 point blank shotgun kills (level 5 in Take It All) and Missile Magnet became "discovered" after I got 200 splash damage rocket launcher kills (level 5 in Collateral Damage). I ended up grinding these two challenges in the first half of the Titan Industrial Facility where a lot of torks spawn. I suggest trying to focus on point-blank shotgun kills as you play through the game so you won't have to grind so many.

Conveniently, after I reached level 5 in Take It All and Collateral Damage, the newly "discovered" challenges had their progress retroactively updated so I didn't even have to work on them- they were already completed to level 1 or higher!

The rest of the initially (undiscovered) challenges became available for me through normal play without needing level 5 completion in something else. I don't have any other weapon challenges completed to level 5 so they may require completing another related challenge to level 1 or 2.

Most of the challenges are self-explanatory. Here is the list of level 1 requirement for each:

Low Gravity
Slampage!: Kill 5 enemies with slam attacks
Dragon Punch: Deal 5000 melee damage while in the air
Eagle Eye: Get 50 critical hits while in the air
Death from Above: Kill 50 enemies wile in the air
Roget Slamjet: Deal 2000 damage with slam attacks
Boosted: Perform 50 air boosts

Grinder
Master Chef: Discover 2 grinder recipes
Greater Than the Sum of its Parts: Obtain 20 Luneshine weapons from the Grinder
The Daily Grind: Perform 50 standard grinds
This Time for Sure: Perform 10 Moonstone grinds

Enemies
Aim for the Little Ones: Kill 10 Opha's spawned Putti
Pest Control: Kill 25 torks
Takin' Out the Trash: Kill 5 tork badasses
That Was Unpleasant: Kill 25 shugguraths
Space Dead: Kill 25 scav outlaws
Die, Moon Jerks: Kill 75 scavs
It Wasn't Yours, Anyway: Kill 1 scav jet fighter
The One That Says B.A.M.F: Kill 10 scav badasses
Exterminator: Kill 25 rathyds
Gift That Keeps Giving: Kill 1 Swagman
Big Game Hunt: Kill 25 kraggons
Slayer of Titans: Kill 1 kraggon badass
Dose of Death: Kill 10 enemies infected with space hurps
Not So Tough Now: Kill 25 Eridian Guardians
More Where That Came From: Kill 2 Eridian Guardian bosses
No Suit For You!: Kill 10 Lost Legion powersuits
Get Some!: Kill 50 Lost Legion Infantry
Crash & Burn: Destroy 1 Lost Legion jet fighter
Kiss My Badass: Kill 5 Lost Legion badasses

Elemental
Some Like it Hot: Deal 5000 damage with incendiary DoT effects
Watt's Up?: Deal 5000 damage with shock DoT effects
Frost Bite: Deal 5000 damage with cryo DoT effects
Out with a Bang: Kill 20 enemies with explosive damage
Toxic Takedown: Kill 20 enemies with corrosive damage
Way of the Enkindling: Light 25 enemies on fire
Chemical Burn: Deal 2500 damage with corrosive DoT effects

Loot
Aaaaaand OPEN!: Open 10 treasure chests
Rare as Rocking Horse...: Loot or purchase 5 blue items
A Chunk of Purest Green: Loot or purchase 25 green items
Day for Every Occasion: Pick up or purchase 10 weapons
Scrounging Around: Open 50 lootable crates, lockers, and other objects
Purple Haze: Loot or purchase 3 purple items
The Happiest Color: Loot or purchase 1 orange item
Junkyard Dog: Loot or purchase 50 white items

Money and Trading
Impulse Shopper: Buy 1 Item of the Day
Pawn Broker: Sell 50 items to vending machines
Mr. Money Pits: Collect 5000 dollars from cash drops
Mom Would Be Proud: Save 10000 dollars
Trade Negotiations: Trade 1 time with another player
Over the Moon: Purchase 25 items with Moonstones

Vehicle
Fender Bender: Kill 5 enemies by ramming them with a vehicle
Improvise, Adapt, Overcome: Kill 10 enemies with a turret or vehicle-mounted weapon
Splat 'n' Slide: Kill 1 enemy by power-sliding over it in a vehicle
Road Warrior: Kill 5 enemies while in a vehicle
Pancakes for Breakfast: Kill 1 enemy with a Stingray slam

Health and Recovery
Soup's Up: Get 1 second wind by killing an enemy with a corrosive DoT
Had a Bit of a Shocker: Get 1 second wind by killing an enemy with a shock DoT
There Can Be Only... Me: Get 1 second wind by killing a badass enemy
Doctor Feels Good: Recover 1000 health
Better You Than Me: Get 10 second winds by killing an ememy
Up Unt at Zem: Revive a co-op partner 5 times
The Phoenix: Get 1 second wind by killing an enemy with a burn DoT
Rollin' the Ice: Get 1 second wind by shattering a frozen enemy

Grenades
Big MIRV: Kill 10 enemies with MIRV grenades
Sprayowee: Kill 25 enemies with Area-of-Effect grenades
Home Nade Cookin': Kill 10 enemies with grenades
Betty Boom: Kill 10 enemies with Bouncing Betty grenades
Pass the Chianti: Kill 10 enemies with Transfusion grenades
See Ya on the Other Side: Kill 10 enemies with singularity grenades

Shields
Nova Say Die: Kill 5 enemies with a Nova shield
Amplitude Killuation: Kill 5 enemies while buffed by an Amplify shield
That'll Learn Ya: Kill 5 enemies with reflected damage from a Spike Shield
Wet Work: Kill 5 enemies while buffed by a Maylay shield
Ammo Eater: Absorb enemy ammo 20 times with an Absorption shield

Rocket Launcher
Missile Magnet: Kill 5 enemies with direct hits from rocket launchers
Punker Buster: Kill 5 shielded enemies with one rocket each
Get a Rocket Up Ya: Kill 10 enemies with rocket launchers
Hand of God: Kill 25 enemies from long range with rocket launchers
Magic Missile: Get 2 second winds with rocket launchers
Collateral Damage: Kill 5 enemies with rocket launcher splash damage
Note: You must complete level 5 in Collateral Damage to "discover" Missile Magnet!

Sniper Rifle
Critical Reception: Kill 10 enemies with critical hits using sniper rifles
Windage Adjustment: Get 2 second winds with sniper rifles
Sharp Shooter: Kill 20 enemies with sniper rifles
Penetrating Wound: Kill 5 shielded enemies with one shot using sniper rifles
Melon Splitter: Get 25 critical hits with sniper rifles
Ol' Skool: Kill 5 enemies with sniper rifles without using the scope/ironsights
Clean and Simple: Kill 5 unaware enemies with sniper rifles

Assault Rifle
Assault with a Deadly Weapon: Kill 25 enemies with assault rifles
Assaulty Dog: Get 5 second winds with assault rifles
Hot Lead Injection: Kill 10 enemies with critical hits using assault rifles
Crouch Potato: Kill 25 enemies with assault rifles while crouched
Aim to Please: Get 25 critical hits with assault rifles

Laser
Battle Star: Kill 10 flying enemies with laser weapons while in the air
Aggressive Lasik: Get 25 critical hits with lasers
Light 'em Up: Kill 10 enemies with critical hits using laser weapons
I See the Light: Get 2 second winds with laser weapons
Pew Pew: Kill 25 enemies with laser weapons

SMG
Bring the Pain: Get 25 critical hits with SMGs
Dinky Death Dealer: Kill 10 enemies with critical hits using SMGs
And Stay Down!: Get 2 second winds with SMGs
Nice Spray Job: Kill 25 enemies with SMGs

Shotgun
Shotgunning the Breeze: Get 2 second winds with shotguns
Hello Uncle Buckshot: Get 50 critical hits with shotguns
Take It All: Kill 10 enemies from point-blank range with shotguns
NOTE: You must complete level 5 in Take It All to "discover" Over Achiever!
Boomstick Boogie: Kill 25 enemies with shotguns
Over Achiever: Kill 10 enemies from long range with shotguns
Shotty Workmanship: Kill 10 enemies with critical hits using shotguns

Pistol
Trigger Happy: Kill 25 enemies with pistols
Pistoleer: Get 25 critical hits with pistols
Magnum Maestro: Kill 10 enemies with critical hits using pistols
Gunslinger: Kill 10 enemies shortly after entering ironsights with a pistol
Pistol Whipped: Get 2 second winds with pistols

Melee
Martial Marshal: Kill 25 enemies with melee attacks
Captain Cutty: Kill 20 enemies with melee attacks using bladed guns

General Combat
Projectile Proliferation: Fire 5000 rounds
Barrel of Laughs: Kill 10 enemies with stationary barrels
One Man's Trash: Deal 5000 damage with Tediore reloads
Throw Me the Money: Kill 5 enemies with Tediore reloads
Comet Crash: Shatter 5 frozen enemies with falling damage
Ice to Meet You: Shatter 20 frozen enemies with weapons
Last Gasp: Kill 10 enemies by asphyxiation
Day of the Dead: Kill 250 enemies during the day
Executioner: Kill 20 enemies with critical hits
Action Hero: Kill 25 enemies using your Action Skill
Having Trouble Breathing?: Shatter 25 enemy oxygen masks
Dark Sider: Kill 25 enemies at night

Miscellaneous
Little on the Side: Complete 10 side missions
The Duelist: Win 1 duel
OC/DC: Complete 5 optional mission objectives
We Have a Contender: Complete 5 challenges

Specific advice

For Grinders: I found these to be the most annoying challenges to complete. You need tons of white, green, and blue weapons to grind. You also need tons of Moonstones for Moonstone grinds and to help get Luneshine weapons.

I ended up exploiting a glitch and the save system to get enough resources to complete these challenges.

For getting enough weapons, I first collected four grindable sets. I had three blue pistols, three green pistols, three green lasers, and three white lasers. I gave these 12 weapons to a level 1 character on a second profile. I then copied that character from my HDD to a memory unit and to a USB flash drive. Next, I'd load a split screen game with my main character and one of the copies of the character from the second profile. I'd drop all the weapons, then bring in the other copied character and drop the weapons again. I'd then grind all those weapons with my main character. Then I'd dashboard, re-copy the character from the HDD to the memory units, and repeat the process. It was a little time consuming but the quickest method I could come up with. I probably could have sped up the process if I got some moonstones on the second profile character to expand his backpack so that he could hold more than 12 weapons.

For Vehicles:
Splat 'n' Slide: Kill 1 enemy by power-sliding over it in a vehicle
-This one was annoying. You power-slide in a vehicle with RB. You have to be moving somewhat sideways as you run over the enemy for it to count.

Unconfirmed But EASIEST Solution for Xbox One
The below portion of the guide in quotes is adapted from the solution by Gryffic Anubis, from the Borderlands 2 Guide.
"The above solution is great for those starting the game over again but for those of you who want to pop this achievement with a character that has completed the above list, an easier method is to just complete the next level of any random challenge that takes your fancy and pop achievement."
Although I can't confirm this works for the Xbox One version of Borderlands: the Pre-Sequel, I just used it last night to unlock the equivalent achievement for Borderlands 2 Xbox One version. I simply took my uploaded character that I completed all challenges with on the Xbox 360, and completed Level 2 Revives with pistols. Logic would indicate it would work for Pre-Sequel too, therefore making this the EASIEST solution.

Confirmed XBOX One Solution by Lambstein

If you are starting Borderlands: The Pre-Sequel on the Xbox One from scratch, with no game save crossover from the Xbox 360, then all the information you need is above.

This portion of the guide is SPECIFICALLY for those individuals who fit these 3 criteria:
1. You own and have played Borderlands The Pre-Sequel for the Xbox 360
2. You have NOT achieved the Challenger achievement for the 360
3. You still need the Challenger achievement for the One

The following idea and steps will work, and could potentially save you HOURS, if you fit the above criteria.

So, here is how I unlocked the Challenger (Xbox One version) in less than one minute after uploading a character:
1. Complete all level 1 challenges EXCEPT for 1 on the Xbox 360 version (For me, it was getting 749 out of 750 on Take It All. 750 unlocks the undiscovered shotgun challenge, Over Achiever.)
2. Upload this character using cloud saves, like you normally would for use on the Xbox One.
3. Go to the Xbox One, download the newly uploaded character, I selected the Save As New option.
4. Continue the character's progress (at the main menu of the game in the Xbox One, select "Continue").
5. Complete the last bit of challenge. (For me, it was shooting one more enemy up close with a Torgue shotgun)
6. Challenge completed, Achievement unlocked. (In my scenario, I automatically earned 50 Bad Ass rank for completing Take It All level 5 going from 749 to 750 up-close kills, and then I also unlocked and then completed several levels of Over Achiever. The game has been recording your "undiscovered" challenge progress even if it hasn't been visibly tracked.)

I know this solution is a little late, but I thought I might be able to help some people. I know that by getting my Xbox 360 character to the brink of the achievement, and then transferring it over to the One, I saved many hours of needless repetition.

This is for the grinder section:

I did this solo but can be done easier in co-op

First of all you need a high level character(I was level 61) with 100 moonstone and a low level character (when they first enter Concordia and have access to the weapons locker)

Now load your high level character and place 4 weapons of high value into the weapons Locker.Now save and quit and switch to your low level character(mine was nisha level 6). Take out the the high level weapons and sell them and you'll now have enough money.Next buy at least 4 white weapons(the levels will vary from 3-6 in most cases) now place them in the weapons locker save and quit.

Switch back to your high level character,take out the low level weapons and now bring them to the grinder and now when you do the moonstone grind it will cost between 3-5 moonstone (depending on the weapon level)

I found this easy to do as all I had left for the challenges was the moonstone grinds. Hope this helps

Ok this for weapon grinding. If you beat the game and did all the side quests just start a new game and do "Home Delivery" it is right after you get the AI and meeting pickle. You have to finish the treasure hunt with Pickle first. Then home delivery is unlocked at Concordia start it up there will be a point where they ask you to freeze and capture the threasures instead kill them there is no limit of enemies and if you have it as coop you can exist to Concordia and grind and restock real quick before getting at it.

To beat the challenges with the grinder machine to get so many luneshine machine.
First you need to get the grinder machine up and running by doing a side quest. Then summon a new player as coop. Have them drop their weapons. (It is easier if you have your weapons stored except the weapons you are using until you are done with this). Keep summoning up coop until you maxed out your spots I recommend have a friend or create a character with enough storage to easily do the clone weapon cheat to make this faster.

**Luneshine Weapons / Moonstone Grinds**

I did this once I'd done the other Achievements (all I had left was Level 50 and complete Challenges) and I'd recommend leaving it until last so you're not worrying about holding on to trash weapons or taking up bank space.

I was level 38 and running the Titan Robot Production Plant for Moonstone (whilst knocking out a few other challenges - Collateral Damage, Battle Star, Take It All! and it's a great place to get Comet Crash imo). It's a relatively quick way to get Moonstone too.

I'd recommend grabbing any White and Green Assault Rifles, SMGs and Pistols that drop from kills and also from the chests at the end of the run then using those for your Luneshine Grinding. Most of the drops for me were Level 15 or 16 and the Moonstone grinds cost 15/16, which isn't too bad in the grand scheme.

I alternated between grinding weapons and Moonstone to mix it up a bit or whenever my inventory was full.

Once you're ready to do some grinding, head to Concordia and throw three of the same type and colour of weapon in the Grinder (for example 3 Green Assault Rifles or 3 White Pistols, etc), hit X to Moonstone grind and if the weapon that comes out of the Grinder is not Luneshine, immediately quit to the dashboard, boot the game back up and try again. Once you do get a Luneshine though, you're going to want to do a lap or two around the Concordia spawn point until you can force a save. Once you see the save icon pop up, head back over to the Grinder and try again. Rinse/repeat.

I'm aware there are many solutions to this but this was the fastest method for me and the least boring. I am also aware I'm a little late to the game, but somebody might find this useful so I thought it was worth writing down.