Starlit Mantle

The protection blue almost never has to pay to keep. Flash turns this into a combat trick wearing an Aura's clothes: hold up two mana, and when an opponent points removal at your creature, cast it in response so the hexproof trigger resolves and fizzles the spell before it can bite. Where blue's usual reactive answer is a counterspell (a one-for-one that leaves your creature naked to the next threat), this saves the body and leaves an enhancement behind. That is the wrinkle worth noticing: the hexproof is a single turn's shield, but the Aura and its +1/+1 persist, so a card that spent one moment as a reactive save is also a permanent buff you can cast on your own turn when nothing is threatening it. The reactive mode still asks you to represent mana, as any instant-speed answer does; what it does not ask is that you commit to a hard counter or a dedicated protection spell that does nothing once the danger passes. Because it flashes in, an opponent can never sequence around it the way they would around a face-up Aura already on the board; the mere threat of a two-mana response can freeze a removal spell in hand. The mana you hold up is never wasted: cast reactively it saves a creature, cast proactively it improves one, and it is the same card either way.