Powerbalance

The mirror-match tax nobody asks for: your opponent's own spell hands you a free cast, provided your library's next card happens to share its exact mana value. That matching clause is the entire engine, and it is a far tighter leash than "cast something for free" suggests. You are not casting whatever you want; you are casting whatever gets revealed, and only when the numbers line up against a spell you had no hand in choosing. Building around it means warping a deck toward a single mana value so the coincidence stops being a coincidence: a curve stacked on twos, say, so every two-drop the opponent throws down risks flipping one of yours back for nothing. The reveal is optional at both steps, so a whiff costs you only information, but the ceiling belongs to an opponent who can play around it simply by casting spells at values you have not loaded. It rewards a hostile symmetry: the more the two boards resemble each other, the more the enchantment fires, which makes it a poor fit for the aggressor and a natural punish against an opponent playing the same game you are. What lands off a successful hit is uncapped by mana value, bounded only by what you have packed at the matching cost, and that is where the real deckbuilding tension lives.