Fearfull Nights is a Modpack with alot of horror styled mods like true darkness, what makes your wolrd completely out of light at night, unless you have a torch that lites your world with brightness when you hold it in your hand. Fearfull Nights also adds alot of horror mobs and entities to your world of darkness like all the fanf characters, slenderman, sirenhead and all the dwellers like the cave dweller, night dweller and midnight dweller.
It is recommended to play this modpack in singleplayer at night to get your scare meter upwards, but if you want to play with another player you can.