Stasis

The original lock piece, and still the purest expression of the idea: untap steps are a resource, and an enchantment can simply switch them off for everyone. The cost structure is what makes Stasis a puzzle rather than a win condition. Two mana to deploy is trivial, but the upkeep tax of a single blue means the Stasis player is also frozen, paying a mana every turn to keep the lock running while their lands stay tapped. Solving that asymmetry is the entire deckbuilding exercise: Howling Mine to refill the hand the opponent cannot empty, Kismet to make sure the lands they do get come in tapped, Black Vise to clock them while they sit on a useless grip, and any number of untap tricks (Boomerang on your own Island, creatures that untap lands, the infamous Chronatog clock) to keep paying the blue without going broke. Few cards in Magic's history have generated so much rules-lawyering at the kitchen table, because Stasis does not end the game; it suspends it, and then the two players negotiate, in mana and life totals, who breaks first. It is the archetypal prison enchantment, the ancestor of every Winter Orb deck and every hard-lock build since, and the reason "skip your untap step" has been treated as a near-unprintable phrase in design ever since.