Counterflux

The genius is in the escalation clause. As a three-mana counterspell that itself can't be countered, this is already a sturdy answer to control mirrors and to the kind of stack wars where a vanilla Cancel gets traded away before it does its job. But overload reframes the whole card: pay one more, and "target spell you don't control" becomes "each spell you don't control," turning a single-target answer into a stack-wide sweep against a storm turn or a fistful of cantrips going off at once. That mode is asymmetric by construction, sparing whatever you have on the stack while sweeping everything the opponent put there, which is the difference between a panic button and a true blowout. The restriction that pays for all this lives in the targeting: it only touches spells you don't control. So it is no way to redirect or rescue something already cast; its protective work is done purely by negation, answering the opponent's interaction (which you don't control) so your spells resolve. This is a counter built to win the fight about counterspells, the answer to the answers, where "can't be countered" is the load-bearing line and the counter-the-spell text is almost secondary. The overload keyword, designed to give instants and sorceries a small-or-large dial, rarely found a cleaner home than turning one counter into many.