Here is the Requirements for the Gunslinger mode in Extras, complete these tasks to unlock art for that specified level.
Wrong Train AnimaticComplete The Wrong Train with 65% or more Accuracy Enemies 1Complete Boneyard with 65% or more Accuracy Enemies 2Complee Showdown with 20 or more Melee Kills VehiclesComplete Deadfall with 20 or more Headshots Allies art, Bosses ArtComplete Curse Of The West on Shootist Difficulty WeaponsComplete Morning After with 70% or more Accuracy Environments 1Complete Darkwatch Outpost with No Deaths Environments 2Complete Invasion on Deadeye Difficulty Environments 3Complete Curse Of The West in 10 Minutes or less Attract Mode MovieComplete Dead Light Prism with 80 or more Kills Highmoon TrailerComplete Rescue in 15 Minutes or less Rescue Intro MovieComplete Hangtown with 20 or more Headshots Cowboy AnimaticComplete Torture Maze with 30 or more Melee Kills Showdown AnimaticComplete The Right Train on Shootist Difficulty Evolution of JerichoComplete the Single Player Campaign on any difficulty Darkwatch ArchivesComplete all Gunslinger levels on Deadeye
