True Dixon Achievement
Complete a Marked Destination on the Map Using Only the Crossbow
You get the Crossbow after Barksdale in which Merle goes to meet up with his old gang. The missions following Barksdale are quite tough and laden with walkers so it may be best to do a marked destination on new game+. What you need to do in order to unlock this achievement is use only the crossbow to kill walkers in an entire level. It's believe that executions still count toward only the crossbow being used.