To put it simply, you have no detail to work with, in any of your points, whether it be your Narrative or your Pitch. Not to mention, you're also missing a hook, which is arguably the most important thing in any article. With no details, no one has anything to critique, other than your lack of what appears to be imagination. To be blunt, this has no chance of getting any kind of greenlight until this gets a major rework.
Now, I'll leave my own questions for your concept.
A Shadow that attracts people with it’s beautiful piano noise, and kills them
Couple questions off the bat, what is the origin of the shadow? Is it a ghost, or some random entity with no apparent origin? Where does the piano emanate from? To follow up with ParmesanDealer, why does it kill? More importantly, how?
The different music it plays and it’s appearance
I feel as though both of these attributes are in the wrong place. The different music it plays would be a mild hook, and the appearance belongs in the pitch, but regardless you haven't alluded to what it actually looks like.
Why are rarely any of the Recent SCPs monsters like the shy guy?
This is a question I asked someone a while back, so I understand where you're coming from. The best explanation that I can give, is this:
I was once told by a reviewer, "Scary creatures that don't kill people or kill people solely out of self-defense have become very common both on the site and elsewhere, so your anomaly cannot stand on that idea alone." Aside from that, authors don't need to write articles about something scary or something that kills to be successful, and everyone knew that even in the beginning. Take for instance, SCP-007, The Abdominal Planet, or even another like SCP-163, An Old Castaway. Another example I have, was a quite interesting concept page I encountered a while back, of a flying brick wall that was hidden under Easter Island.
The way other reviewers see it, SCP's that kill have been so commonplace that they've become boring. While I don't entirely agree with that, unfortunately I'm not in charge of what's popular/interesting, so we all gotta make do.
Anyways, that's all from me. Send me a PM if you make a response here, I'll take a look and reply if need be. I bid you good tidings!