Prepare

万智牌机制

Casting the copy of the prepared spell works just like casting any other spell. You have to pay its cost, and you have to follow the timing rules put in place by its card type. If it's a sorcery like Rampant Growth, you can cast it during your main phase if the stack is empty. If you cast a prepare spell from exile, the prepared creature becomes unprepared, meaning it loses the prepared designation.