I think the game’s name is all about what the game is abou, something like “Lights off” (ik it might not be the best name) wouldn’t fit for a game when you’re say in a forest getting hunted by a monster, but might but might fit if you’re in a house and the lights go out or something.
For map I think you should try and limit the players vision, like making a narrow hallway or a door without windows and not a lot of open areas. Also remember that every map doesn’t have to be dark and alone, there are places that can be scary for people even during daylight or in crowded places.
For a monster I also feel like it kinda depends on the game, again if its about being in a forest maybe a human killer wouldn’t go around waiting for people having some super power to see in the dark, instead I’d go for the entire monster being not normal if that makes sense.
Of course everyone finds different things scary but one important thing can be to build tension, like noises, shapes of the monster and fitting music. One important thing to try and stay away from is jump scares, whilst a lot people get scared by them its not really “scary”, you get scared for some time but that time is not for long, obviously you can have jump scares but it shouldn’t purely be jump scares.
Again, everyone is scared of different things but i think some popular things are deep ocean, monster like creatures, ghosts and tight spaces.
sorry for not having . and , in the right places btw