I have a character that is designed to be a scientist and he sees beings that have shadow powers, think Noob Saibot, he tries to explain the phenomena in a scientific way. They beings look human Powers
This started as a comment, and as I got further I realized it might be better as an answer.
Trying to explain shadow-related powers scientifically is... problematic. Shadows aren't objects, they're just areas with fewer photons in them than other areas. A shadow is also a very relative term-- the number of possible light levels is virtually infinite, and a shadow in a bright room might still be pretty well-lit. If you've ever stood outside right after sunset, or even just during an overcast, you'll know what I'm talking about; you're technically standing in a shadow, but there's still plenty of light around you.
To even approach a scientific explanation, you're going to have to define a light level in which your creatures can operate. Dungeons & Dragons uses four basic light levels:
Bright light: Outdoors on a sunny day.
Normal light: Outdoors on a cloudy day, or indoors in a well-lit room
Low light: Outdoors under a full moon, or indoors in a room lit only by a candle
Darkness: Outdoors on a cloudy and moonless night, or indoors at night with no light sources (the game makes no distinction between this darkness and the utter blackness of an underground cavern)
Obviously the game uses these terms in a magic-heavy context, but you will need at least a general idea of the amount of light that prevents your creatures' powers from working. After that, you're still looking at some major Hand-Wavium, because anything vulnerable to photons will be vulnerable to lots of other things too.
Assuming that you want a scientific explanation based on our universe's physical laws, and our understanding of them, the problem with the premise is that shadows are the absence of something, namely light. Now, you could have a creature who can create shadows, and shadow objects like a sword, by collecting photons and harnessing them into a physical form. By taking photons from the area around them, it would create areas of shadow, and an object that appears to be made of shadow. But actually taking a shadow that "exists" and turning it into a weapon, I have a much harder time explaining that. To better explain, your premise would be stronger at night, because the entire Earth is in shadow, thus giving them more "material" to draw from. Where my example would be weaker because there is less ambient light to capture.
As for appearing and disappearing into shadows, I assume you mean some kind of teleportation (enter one shadow, exit another). That's much harder to explain. Again, you could explain it so that it visually appears that's what happens, when realistically they are doing something else, like folding space-time using the energy of light to give them the immense power needed, thus creating shadows. But actually going through a "shadow", in a scientific sense, as we understand them, doesn't make much sense.
I think the best way to explain it is not to consider it as a shadow. I mean: it MAY look like a shadow, but it is not. Think of it as a swarm of self-organizing micro-drones. They could take whatever shape they want (even as flat as the size of a single micro-drone). And they could also group and attach themselves in a 3 dimensional form (a blade for example) to perform some physical interaction with the environment (including kill someone). Besides, if they want to "dissappear", the drones just need to fly away from each others, or they could even change color to blend with the landscape besides them and in front of the observer (some sort of "invisibility").
The challenge here, as was already mentioned, is that shadows are the absence of something. You can fix this by having those supernatural beings MIMIC shadows - think of something that is chameleon-like - and they can also have the ability to appear super flat. If they have the ability to teleport, this suggests that they can control space-time, making it easier for them to appear to have zero thickness, as one would see in a shadow.
