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
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
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
a pop, it's considerably slower especially since it drains all remaining
Nice idea!