Hydroblast

Color hate distilled to its hardest edge: against red, this single mana answers both the threat on the stack and the threat already on the battlefield, countering a burn spell coming at you or destroying a red permanent that has landed. The modal split is the elegant part, because one card covers the full lifecycle of a red threat instead of forcing you to choose your moment. The cost of that flexibility is the conditional that makes the rate possible: it works only on red, so a card that addresses one fifth of the color pie can be priced this aggressively without warping anything around it. Pyroblast does the identical work pointed at blue, and the two have shadowed each other through every reprinting since, the canonical hoser pair where the constraint is the whole design. This is a meta call rather than a generic answer. In environments where red is a known, defining presence, maindecking it is reading the room; held in reserve, it is the lever that swings a matchup. When red is the metagame's defining color, an instant that both counters and destroys it for this price is as efficient as interaction gets; when it isn't, the card is dead in hand, and that volatility is the entire point. Hosers do not aspire to be good cards. They aspire to be devastating against exactly one thing and worthless against everything else, and few do it more cleanly than this.