Did this ever cost stamina? Could have sworn it was always magicka. Would be nice with stamina cost though. But im trying to be a firm believer of magicka offense should cost magicka for defense, as it should cost magicka to block magica based abilities, and vica versa for stamina based stuff.
I'm more curious about why did they nerf it?
It used to REDUCE spell damage taken by 50% (which was then absorbed by the bubble). In 1.1.2 it was changed to ABSORB 100% spell damage, which just means it works like every other absorb shield - instantly vanishing when you get damaged anyway.