Challenge

Challenges are special feats that can be completed for bonus experience points in Borderlands, or Badass Ranks in Borderlands 2 and Borderlands: The Pre-Sequel. Most challenges involve killing many of the same type of enemy, using weapons to kill enemies, or using Elemental Damage to kill enemies. Other challenges are based around discovering hidden areas, looting enemies, travelling, and vehicles.

Trivia

 * The Action Skill challenge "Your Kung Fu is Best" is a line taken from the television series The X-Files. The phrase itself is a play on "my kung fu is best".
 * The Enemy Kill challenge "I am become Death..." references those same words spoken by J. Robert Oppenheimer, the "father of the atomic bomb", when interviewed about his feelings on the weapon he had designed.
 * The Shots Fired challenge "Who made that man a gunner?" is a reference to Mel Brooks' spoof of Star Wars, SpaceBalls.
 * The Fire Kill challenge "Hot! Too Hot!" is a reference to Spaceballs when Dark Helmet tries to gulp his coffee.

Borderlands 2
After a patch, challenges can be reset after 85% have been completed.

General Challenges
These challenges can be completed in various parts of Pandora. They have five levels, awarding 1, 5, 10, 50, and 100 Badass Ranks respectively. There are 114 general challenges, excluding DLC.

Location-based Challenges
These challenges are tied to specific locations, and have one level (They are either completed or not). Location-specific challenges award varying amounts of Badass Rank. There are at least 64 location-based challenges. These are also called level-specific challenges because they are tied to a certain 'level' (area). Note that the Eridium Blight challenge ‘Save the Turrets' can be missed.

Trivia

 * The Enemies challenge "Little Person, Big Pain" is likely a play on the title of the television program Little People, Big World
 * The Enemies challenge "Die in the Friendly Skies" is a play on United Airlines' slogan "Fly the Friendly Skies".
 * The Enemies challenge "Another Bug Hunt" is taken from a line in the film Aliens.
 * The Enemies challenge "Skags to Riches" is a play on the cliché Rags to riches which is a phrase used to describe someone who goes from poverty to wealth or from obscurity to fame.
 * The Enemies challenge "You Dirty Rat" is a line of dialogue often attributed to gangster characters portrayed by either James Cagney or Edward G. Robinson, however neither actor ever said this line verbatim in any film.
 * The Enemies challenge "Crystals are a Girls Best Friend" is a play on the title of the song "Diamonds Are a Girl's Best Friend" originally from the Broadway production of Gentlemen Prefer Blondes.
 * The Enemies challenge "You're One Ugly Mother..." is a partial line from the character Dutch portrayed by Arnold Schwarzenegger in the film Predator, referring, of course, to the titular alien.
 * The Elemental challenge "Cowering Inferno" is a play on the title of the 1974 disaster film The Towering Inferno.
 * The Elemental challenge "Say "Watt" Again" is a play on a line spoken by Julius Winnfield, a character portrayed by Samuel L. Jackson in the film Pulp Fiction.
 * The Elemental challenge "I Just Want to Set the World On Fire" is a play on the 1941 song title "I Don't Want to Set the World On Fire" by The Ink Spots. The song has become popularly known as the opening theme for the video game Fallout 3.
 * The Loot challenge "Purple Reign" is a play on the soundtrack album and film Purple Rain recorded by/starring Prince.
 * The Loot challenge "It's Not Easy Looting Green" is a play on a lyric from the song "Bein' Green" in which Kermit the Frog famously laments that "it's not easy bein' green".
 * The Loot challenge "Another Man's Treasure" is taken from the idiom "One man's trash is another man's treasure".
 * The Loot challenge "Call of Booty" is a play on the Call of Duty video game franchise.
 * The Money and Trading challenge "Dolla Dolla Bills, Y'all" is a slight variation on a lyric from the song "C.R.E.A.M. (Cash Rules Everything Around Me)" by Wu-Tang Clan.
 * The Money and Trading challenge "Whaddaya Buyin'?" is likely a reference to the quote said by the vendor in the game Resident Evil 4 when you talk to him to shop.
 * The Money and Trading challenge "For the Hoard!" is a play on words referencing World of Warcraft, where NPCs of the Horde faction will say "For the Horde" after accepting a quest and is a possible achievement for slaying the leaders of the Alliance faction.
 * The Vehicle challenge "Hit-and-Fun" is a play on the crime "hit and run" in which a person driving a vehicle collides with another person or object and then leaves without identifying himself or herself.
 * The Vehicle challenge "Turret Syndrome" is a play on the neuropsychiatric disorder Tourette's Syndrome.
 * The Vehicle challenge "...One Van Leaves" is a play on a line from Mad Max Beyond Thunderdome which notes that the law of battle in the Thunderdome is "Two men enter, one man leaves".
 * The Health and Recovery challenge "Death, Wind, and Fire" is a play on the soul/funk/disco band Earth, Wind &amp; Fire.
 * The Grenade challenge "Whoa, Black Betty" is a lyric from the chorus of the song "Black Betty".
 * The Shields challenge "Game of Thorns" is a play on the title of the first book, "Game of Thrones", in the "A Song of Ice and Fire" series by George RR Martin.
 * The Rocket Launcher challenge "Rocket and Roll" is an obvious play on the musical genre Rock & Roll.
 * The Rocket Launcher challenge "Splish Splash" is taken from the song of the same name originally recorded in 1958 by Bobby Darrin.
 * The Rocket Launcher challenge "Catch-a-Rocket!" is a play on Catch-A-Ride, Scooter's in-game transportation hubs.
 * The Rocket Launcher challenge "Gone with the Second Wind" is a play on the title of the 1936 novel Gone with the Wind by Margaret Mitchell, which was then adapted into the Academy-Award-winning film in 1939.
 * The Sniper Rifle challenge "A Leaf on the Second Wind" is likely a play on the line "I am a leaf on the wind, watch me soar." spoken by the character Hoban "Wash" Washburne portrayed by Alan Tudyk in the film Serenity.
 * The Assault Rifle challenge "Crouching Tiger, Hidden Assault Rifle" is a play on the title of the film Crouching Tiger, Hidden Dragon.
 * The Assault Rifle challenges "This is My Rifle..." and "...This is My Gun" are likely a reference to a scene from the film Full Metal Jacket. However, the former is also the first line of the Rifleman's Creed.
 * The Assault Rifle challenge "From My Cold, Dead Hands" is a reference to a quote made famous by actor Charlton Heston in a speech at a National Rifle Association (NRA) convention in 2000 when he was president of the organization.
 * The Shotgun challenge "Lock, Stock, and..." is a reference to the title of the film Lock, Stock and Two Smoking Barrels.
 * The Pistol challenge "Hard Boiled" is likely a reference to the film of the same name, especially when given that the shoot-outs in the film are largely pistol-based.
 * The General Combat challenge "...I Got to Boogie" is a lyric from the chorus of the 1978 disco song "I Love the Nightlife (Disco Round)" by Alicia Bridges.
 * The General Combat challenge "Afternoon Delight" is a reference to the song of the same name by The Starland Vocal Band and the Rocket Launcher challenge "Skyrockets in Flight..." is a lyric from the chorus of that song.
 * The General Combat challenge "Not Full of Monkeys" is a reference to the children's toy/game Barrel of Monkeys.
 * The Miscellaneous challenge "JEEEEENKINSSSSSS!!!" is a reference to an internet meme from World of Warcraft in which player "Leeroy Jenkins" shouts his name and charges into a boss battle without allowing the rest of his party to prepare.

General Challenges
There are eight general challenges included with Captain Scarlett and Her Pirate's Booty. These challenges must be completed in areas included with this DLC pack.

Location-based Challenges
All location-based challenges award 4 Badass Rank.

General Challenges
There are six general challenges included with Mr. Torgue's Campaign of Carnage.

Location-based Challenges
All location-based challenges award 4 Badass Rank.

General Challenges
There are six general challenges included with Sir Hammerlock's Big Game Hunt.

General Challenges
There are ten general challenges included with Tiny Tina's Assault on Dragon Keep.

Location-based Challenges
All location-based challenges award 5 Badass Rank.

General Challenges
There are eight general challenges included with Commander Lilith & the Fight for Sanctuary. These challenges must be completed in areas included with this DLC pack.

General Challenges
These challenges can be completed in various parts of Elpis and Hyperion's Helios space station. They have five levels, awarding different Badass Ranks. There are 128 general challenges, excluding DLC.

Location-based challenges
These challenges are tied to specific locations, and have one level each (they are either completed or not), rewarding different amounts of Badass Rank. There are at least 80 location-based challenges.

Borderlands: The Pre-Sequel DLC
These challenges are only available for completion by owning the respective DLC.

They are all tied to specific locations, and have one level each (they are either completed or not), rewarding different amounts of Badass Rank.

Trivia

 * The Loot challenge "A Chunk of Purest Green" might be a reference to the television series Black Adder (S2-E4).

Borderlands 3
These challenges can be completed in various locations. They have five levels, each awarding varying ammounts of Eridium.