The short version
The costumes that unsettle people are not the bloodiest. They are the ones with an unfamiliar silhouette, a face that does not move, and a wearer who stays still. Blood is a texture; it reads at two metres and disappears in a photograph. Shape reads across a room.
Silhouette does the work
Anything that changes the outline of a human body — height, shoulder width, the proportion of the head — registers before the brain has identified what it is looking at. That half-second of not-knowing is where the reaction comes from. A perfectly detailed mask on a normal silhouette is identified instantly and stops working.
The pieces in Genuinely Frightening are chosen on that basis: full masks that change the head shape, garments that alter the outline, and nothing that depends on a viewer standing close enough to appreciate detail.
A face that does not move
A rigid mask is unsettling for the same reason a doll is: the features stay fixed while the body moves. Painted faces are more expressive and therefore less frightening — they are the right choice for an evening among friends, and the wrong one if the aim is to unsettle.
The trade-off is real. Full masks restrict vision and breathing, they fog, and they make conversation hard. A costume that works for thirty seconds at a door is not the same costume as one worn for four hours.
Stillness, then movement
The single most effective technique costs nothing: stand still. A figure that does not move is read as an object until it does. Every haunted attraction in the world runs on that principle, and it works just as well in a hallway.
What to avoid
Fake blood on anything you want to keep, because most formulations stain. Contact lenses bought without a prescription, which are a genuine eye risk rather than a cautious warning. And anything that obscures vision while standing near stairs.
Makeup that survives an evening
Fake scars and wounds fail in one of two ways: they lift at the edges, or they transfer onto everything. Both are solved the same way — thin layers, ten minutes of setting time, and setting powder over anything that will touch fabric. A wound applied five minutes before guests arrive will be on someone's shoulder by nine.
Removal is where skin gets damaged. Oil-based remover first, then a normal wash. Scrubbing dry grease paint off with soap spreads it and irritates, and the irritation lasts longer than the evening did.