Twist Allegiance

Most control-swap effects steal one creature and hold it forever, or take an opponent's board for a single decisive turn. This one mutually exchanges every creature both players have, then untaps and hastes the lot of them. That untap-and-haste rider is what turns a symmetric trade into a one-sided alpha strike: you hand over your blockers, take theirs, and swing with a freshly mobilized army the same turn it crosses the table. The catch baked into the wording is that the swap cuts both ways and reverses at end of turn, so the math only favors you if your opponent's board is bigger and more threatening than yours, and if you can convert the borrowed creatures into damage or sacrifice fodder before they return home. It is a Threaten effect scaled up to both players' boards, with the same sorcery-speed clock and the same demand that you cash the rental in before it expires. The seven-mana price tag and the all-or-nothing symmetry mark it as a card built for swing-the-game spectacle rather than incremental value: the kind of spell that does nothing against an empty board and threatens lethal against a full one. The reciprocity is the design honesty here; the creatures snap back to their previous controllers during cleanup, so the borrowed army is a single turn's worth of pressure that must be spent or wasted. Fumble the conversion and you have done nothing but untap your opponent's blockers for them.