Sleep Paralysis

The blue answer to the problem that white solves cleanly and black solves with murder: how do you neutralize a creature without removing it? This locks the body down indefinitely, taps it on the way in for good measure, and leaves it sitting there as a permanent that does nothing. The lineage runs back to Paralyze and forward through dozens of "doesn't untap" Auras, each tuned for a different cost and a different rider. The structural weakness is the same one every Aura of this stripe carries: it answers a creature without trading one-for-one cleanly, since a single bounce, blink, or enchantment-removal spell frees the prisoner and leaves you down a card. That fragility is the price blue pays for refusing to deal in permanent answers; the color is built to delay, not to destroy, and a creature merely held captive can always be liberated. The entry-tap clause is the rider that earns the slot. Without it, a freshly enchanted untapped creature could still block on the following turn; the tap-on-arrival closes that window, stripping the creature of its next attack or block immediately rather than only after its controller's untap step fizzles. With no flash on the Aura, the casting itself is a sorcery-speed commitment, so the tap clause does the timing work the spell cannot. It is a soft lock dressed as removal, which is exactly the compromise blue is supposed to make.