Say my opponent has Elesh Norn on the table and plays Phyrexian Metamorph as a copy of her. As I understand from her Gatherer-page, all my creatures will now briefly have -4/-4.
So my question is now, suppose I have Obsidian Fireheart (or any other elemental with at least 3 toughness) in play along with two Incandescent Soulstokes, then obviously both my Soulstokes die as they have -1 toughness each, but will Obsidian Fireheart die as well? In other words, when exactly during this process does one copy of Elesh Norn leave the battlefield due to the legendary rule?