Mystic Restraints

Flash on a tapping aura is the whole trick: it lets you flash it in before an opponent declares attackers, tapping down a would-be attacker and keeping it locked down every turn after. The double tap of tap-on-entry plus the no-untap clause is the design point, because either half alone is incomplete. A plain "doesn't untap" aura cast at sorcery speed only matters next turn, by which point the creature has already swung; tapping the creature on entry closes that gap, so the answer works the same turn it lands. The result is a soft removal spell that reads as removal in practice: the enchanted creature stays tapped through its untap step, so it typically never attacks, never blocks, never crews, never taps for an activated ability or mana again. It still occupies the battlefield and still dies to wrath effects, but it is functionally a dead permanent. This belongs to the long blue tradition of pacifying threats rather than killing them, the lineage that runs through Claustrophobia and its many cousins. Where most of those variants wait politely for your own main phase, the flash here pries the answer open at instant speed, letting you respond in the empty window of an opponent's combat rather than telegraphing it a turn early. Four mana for a permanent lockdown is a fair rate; the instant-speed flexibility is what justifies the second blue pip.