I could see this definitely being useful. Opponent is splashing a cheap spell (Deflag, Shockwave, Momentum, Reverse Time, etc...)? Now they can only play it every other turn instead of every turn.
Rain of Fire in a rainbow? Costs 10
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now, not as easy to get out.
More importantly in the anti-rainbow sector, getting this on turn 1 or 2 could SEVERELY slow down supernova based rainbows.
Miracle costs 24
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with this.
My favorite effect, however, would have to be that this is the answer to how prominent Fractal has become since its introduction in so many decks. At 16
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a pop, it's considerably slower especially since it drains all remaining
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Nice idea!