5 Mega Polaroids on the field should make a fast shutdown, since the enemy cannot deal with 40% constant decrease in accuracy (without adrenaline). 3 can also be efficient, but works slower. Less than 3 is not very efficient.
But you both got the point of reducing the cost of the upgraded card, so I'm going to reduce it. Eventually it will be as effective as a Dusk Mantle, if not better.
Edit: How does this look?
Compared to the unupgraded, only the cost is reduced. Everything else stayed the same.