When I first heard about turn 0 in the Hulk Flash thread I was very confused couse I had never heard of turn 0 before. A friend says that it's the turn where leylines and such is put into play and that you can play instants in this turn. But I'm still kinda puzzled about this. Is it like a normal turn with except there's no draw phase or main phases or is it just a turn consisting of a single phase? What exactly are you allowed to do in turn 0? Can you respond to a leyline comming into play?
I haven't been able to find any info on this, not even in the Magic Comprehensive Rules, so it seems it's like an undocumented thing.