The Rapier was introduced in the November 26, 2016 hotfix. This gun may have been the Marksman's 13th unofficial weapon. It was later confirmed as an accidental inclusion of a gun they were testing so the reason why it was on Marksman stays unknown.
The gun stayed in the game for 2 patches, and had the image of the Hooligan (The image of Haunter is due to a wrong weapon image for all guns). The gun appeared to supposedly be an unlock for level 6, but was actually set to unlock at level -1, making it impossible to unlock for the average player.