Most mods will provide instructions for installation. Then make sure to put the file into the modded folder. To install Manually, Find the mod on the nexus or another Darkest Dungeon modding site and download the file.
To install from the steam workshop, just find the mod on the page you want and then click subscribe. One way is through the steam workshop and the other is the manual installation method. There are currently two methods of installing mods. *This page is under construction and may fuse with the Modding article in the future.
