These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Fridge Brilliance: According to pseudoscience, the standard weight of a soul is 21 grams. When you have collected all the memories, your weight equals... 21g.
Fridge Horror: Every time you lose a life, the message "Boy #X faded away at Floor Y..." This could mean that every time you die, another boy has his shadow cut away from him and has to climb the tower again.
Nightmare Fuel: The Shadow Soul right from the very beginning with the great buildup to its first appearance all the way through the Dark Tower. It may not feel as scary at the very end since this time you can actually fight back.
The Woobie: The shadow. All he wants is to get his body back, and to do that, he has to climb a tower full of traps, puzzles, and shadow monsters. And when he does get to the top, his body is gone.
When he gets the Gatekeeper's Sword and can enter the real world, he says, "It hurts. If I don't get back to the world of shadows, I will die." So every time you go through a light gate, the boy's shadow is in pain.