Here are the requirements for the Gunslinger mode in Extras, complete these tasks to unlock art for that specified level.
Allies art, Bosses Art
Complete Curse Of The West on Shootist Difficulty.
Attract Mode Movie
Complete Dead Light Prism with 80 or more Kills.
Cowboy Animatic
Complete Torture Maze with 30 or more Melee Kills.
Darkwatch Archives
Complete all Gunslinger levels on Deadeye.
Enemies 1
Complete Boneyard with 65% or more Accuracy.
Enemies 2
Complee Showdown with 20 or more Melee Kills.
Environments 1
Complete Darkwatch Outpost with No Deaths.
Environments 2
Complete Invasion on Deadeye Difficulty.
Environments 3
Complete Curse Of The West in 10 Minutes or less.
Evolution of Jericho
Complete the Single Player Campaign on any difficulty.
Highmoon Trailer
Complete Rescue in 15 Minutes or less.
Rescue Intro Movie
Complete Hangtown with 20 or more Headshots.
Showdown Animatic
Complete The Right Train on Shootist Difficulty.
Vehicles
Complete Deadfall with 20 or more Headshots.
Weapons
Complete Morning After with 70% or more Accuracy.
Wrong Train Animatic
Complete The Wrong Train with 65% or more Accuracy.
Blood vision
Press R3 to activate your blood vision.
Defeating Banshees
Be careful while fighting banshees. If you cut off their arms and they still live, they will fire non-stop energy balls at you.
Defeating Lazaurus
While fighting Lazaurus for the final time, hide in the house when he is using his twister move; it will shield you. Also, when he shoots his fireballs and smoke clouds, shoot them; they will blow up and you will be unharmed.
Ducking
Press L3 to duck.
Evil deeds
Blood Frenzy: Adds a supernatural boost to hand-to-hand combat.
Black Shroud: Covers you in a black shroud of darkness that hurts enemies when they attack for a short time.
Immortal Friends: No matter how many times you shoot Cassidy or Tala, they will not die.
Soul Stealer: Sucks the souls right out of living enemies (can be used at a distance).
Turn: Turns some enemies against each other for a short period of time.
Good deeds
Fear: Some enigmas will run scared for a short time.
Mystic Armor: Strong armor (possible 0 damage) for a short time.
Silver Bullet: Infinite and more powerful bullets for a short time.
Vindicator: Shoots a chain of lighting that instantly destroys most small monsters.
Hold two weapons
Press Down to switch to your second weapon slot. This is useful if you are saving a rail rocket or shotgun. Also, press Up to switch between dynamite and splitter grenades (if available).
Quick clear
While fighting a group of enigmas and there is a Dark Mark (Evil Tree), quickly destroy the tree before fighting any enemies. When it is destroyed, it will shoot a shockwave, instantly destroying all enemies in that area.
Rapid fire pistol
Hold down the fire button (R1) on the pistol (Redeemer) to fan it, or shoot in rapid fire.