Dispel

The narrowest counterspell that earns its place by being narrow. Negate stops a wider swath, Spell Pierce taxes early, but a single blue mana that answers only instants buys you something the broader options cannot: a price low enough to leave open under a tapped-out board, and a target so specific that it slips beneath the taxes and tempo costs the wider answers carry. The design logic is a trade of breadth for floor. By restricting the catch to instants, the cost can fall to the absolute minimum, and against the decks that live at instant speed (burn, control mirrors leaning on counter wars, combo lines assembled on the stack) that minimum is the whole point. It wins counter-counter fights for one mana while the opposing answer cost two or three. The limitation is also the failure mode: against a deck running no instants it is a dead card, and the line between "perfect answer" and "blank" is drawn entirely by the opponent's spell types. That binary is what makes it a sideboard specialist rather than a maindeck staple in most eras. Dispel is the purest illustration of a recurring blue-design idea: that a counterspell's value is set less by its rate than by the exact shape of what it can and cannot stop.