that will either grant those that look into it what they truly desire or manifest what they truly fear.
We get a loooooooot of mirrors submitted to and deleted from the site. What you have here isn't really unique enough to do well, I'm afraid. There's already the Mirror of Erised from Harry Potter that plays on this trope, as well as lots of scary mirrors that mess with people (Oculus plays with that approach a bit). Plus all the stuff listed in the trope pages: https://tvtropes.org/pmwiki/pmwiki.php/Main/MagicMirror /
At this point the shadow can be seen approaching in any mirror the subject looks into. The shadow will ultimately envelop the reflection of the subject and disappear.
Okay, but why is there a shadow at all? And why does it eat people's reflections?
Shortly afterwards the subject’s greatest desire or fear will become a reality.
What if the greatest fear is something like outliving all your friends into old age? Or never finding true love before you hit your 70s? Or your beloved dog never returning after being lost? Similarly, what if the greatest desire is something impossible, like someone being brought back to life after they've been cremated or being able to change something that happened in the past?
I don't think you have enough unique material here to make an SCP, sorry. If you really want to try to make this work, consider reading through this essay on adding depth to the classic overused "thing that does a thing" SCP formula: http://www.scp-wiki.net/things-what-do-a-thing-an-essay-on-things but it may take a lot of work to make this mainsite-ready.
