There's a number of items out there that the player must declare are being used at the start of the opponent's magic phase (Hell Heart and Vortex Shard come to mind). So, should this happen before or after the wind of magic is rolled? Most of the time, at my store anyway, the only indication that the magic phase has begun is one guy abruptly flinging two die at the table and yelling "Winds of Magic!" a nanosecond before they bounce- not really a whole lot of chance to declare an item if you need to do it before. On the other hand, knowing how many power dice have come up is a HUGE advantage if you're deciding whether or not to mess with (or delete) the other guys' magic phase. Anyone know of any rulings on this, one way or the other?
In all the games that I have ever played, the other player (and myself) declare that we are starting the magic phase before we roll the dice. I have participated in two tournaments during my time playing where we did the exact same thing. I have not seen it written anywhere, but to me it just seems like a courtesy to do it that way. Sure, I have had the vortex shard used to shut down my magic phase (usually when I roll extremely well on the winds of magic).
winds of magic is at the start of the magic phase. when there is a rules dispute as to the order of things happening (in this case both things happen "at the beginning of the magic phase") the player whose turn it is decides. if they start the phase by randomely flinging two dice, as you so humorsly described, then they are essentially declaring that winds of magic is going first. it is not your responsibility to interrupt their style of play nor disclose your list. if they simply play that quick, theres not much you can do really.