Encase in Ice

A color-hate Pacifism aimed at the two colors blue is least willing to trade blows with. The split between its two restraining clauses is the whole design: the enter trigger taps the creature the moment the Aura lands, denying a future attack, while the no-untap clause pins it on every turn that follows. Because it can only enchant red or green creatures, it belongs to a long line of asymmetric removal that trades flexibility for efficiency, doing nothing whenever those colors are absent and shutting off an attacker indefinitely when they are present. Flash is what lifts it past a clunky Aura. Rather than committing sorcery-speed mana to neutralize a threat on your own turn, you can hold the mana up like a counterspell and drop it during combat, on an end step, or in response to a freshly resolved bomb before it takes a swing. The instant-speed window also changes the math against untap-based tricks: catch a creature already tapped from attacking or activating, and the no-untap clause locks it there without the enter tap ever mattering. That timing flexibility is the real separator from earlier color-restricted lockdown Auras, which asked you to spend the turn to answer the turn.