Hylophobia

This is a horror based mod with horror entities and dwellers that you try to survive. There are also shader packs like Insanity Shader that try to up the fear level and make the game more challenging. There are over 80 mods, including mods like Cold Sweat to make the game seem more realistic and harder, as well Alex's Mobs to give an even more sense of realism. In short, this modpack is a difficult and fun one to play solo or with friends.