This direction is shown with cards like Laelia, the Blade Reforged and Wild-Magic Sorcerer, or Prosper, Tome-Bound if you add black mana
Anything that is looking for the "natural result" is looking for the number shown on the face of the die before these modifications
Plus, it has a nifty additional effect that the controller of the spell it counters can't cast anymore spells this turn
It is hard to know how important it is to keep your land count up compared to the spell you are considering countering
This is a quick and easy way for a player who's behind to suddenly catch up and turn the tables, but the Mirror is a bit costly as compensation for that kind of power
So yeah if you want to open packs of this set, and you probably do, make sure you buy a sealed box and that you do it before the end of the first distribution wave