Once a spell is not successfully cast you can't cast it again, so you can't spam it that way like that. I agree the new rules are ridiculous but you can't spam spells, just like you can't really one dice fireballs, because if you role 1-3 on that one dice it auto-fails, and then you can't recast it.
Edit- you also can't recast spells with a 15+ casting cost, which purple sun does so another way that prevents from spamming that particular one (as well as all killer spells I believe) ...
Warhammer legend 1990 -2015. RIP Warhammer Fantasy. F**k GW
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