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Foolish little boy you just activated my face down trap card.
Wow, this is overhyped!
Yes, it's good with "Avenger of Zendikar". But then "Avenger of Zendikar" is usually game-winning all on its own.
"Mystic Reflection" needs a good target and an effect that creates a bunch of creature tokens all at once to be good. Note that, if the target is gone before "Mystic Reflection" resolves, it fizzles (aka is countered for lack of targets), which often will be a 2-for-1 for the opponent.
Apart from creating copies of good creatures you can 'counter' a big creature (or planeswalker) play of an opponent, but only if there's a weak creature somewhere on the battlefield. Yes, you can possibly 'elk' an opponent's commander before it enters play, which is probably good in cEDH, but less important in more casual settings. And the opponent will get something and it's not too hard to get the commander back (flicker, bounce, sac, kill, wipe, ...).
This really doesn't sound like a 10+ EUR card, more like 0,1 to 2 EUR. It's also not mythic.