The following scenario is hypothetical but something that theoretically could happen in a high stakes Vintage tournament (damn you, Brian Kelly).
Player A activates Oath of Druids, targeting player B, and putting Gisela, Blade of Goldnight into play. Player A passes the turn to player B, who casts Phyrexian Metamorph. When Phyrexian Metamorph resolves, player B chooses Gisela and passes the turn back to player A. Player A chooses not to use Oath of Druids, proceeds to the declare attackers step, and moves their copy of Gisela into the red zone as an attacker. Player B blocks with the Metamorphed Gisela. Player A asks if combat damage occurs, Player B says yes. Player A picks up their copy of Gisela and places it into their graveyard, then proceeds to cast a Preordain in their second main phase. Player B picks up their copy of Gisela and places back among their other creatures.
As player A is resolving Preordain, player A notices that Gisela is still on the battlefield and says that it should be in the graveyard. Player B responds by saying
"The player whose permanent is being dealt damage chooses the order in which replacement effects are applied. The optimal line and the way it is handled on MTGO is that the damage reduction is applied first, reducing the damage dealt from 5 to 2 (Gisela rounds up the amount of damage prevented). Your Gisela's effect will then double it to 4 and my Gisela will survive combat. As for your Gisela, I assumed you chose to stack the replacement effects in the opposite order so that 5 damage is doubled to 10 and then halved to 5 since you placed the card in your graveyard."
At this point, a judge is called.
As a judge, how would you handle this situation? Would it be different if the players would be reversed (i.e. does turn order matter)?
Note: This is not a line of play I would make, recommend, or endorse. I am however curious how the rules would be applied if this situation were to happen.