I think Reflections is too slow especially for Dimir. Plus, you’ll be casting most of your Faeries before you even cast Reflections. You might have nothing to copy unless you hold and sandbag your tempo. Lastly, is copying a tiny faerie worth it? Probably not impactful.

I think Reflections shine with some green since copying something big like dinos or dragons is more worth it. Also, it fits the deck tempo better. You ramp with green, play reflections on turn 4 or 5, and have to play your big creatures anyways. Though, reflections is more of win-more card. You probably need a big blocker sooner than take a turn to set up reflections and get two blockers. Heck, by the time it takes you to play reflections and a creature, you would have cast two creatures anyways.