Part of Storyline
If multiple events are competing to be added at the same point on the storyline, the active player adds all of their events first, in the order of their choice. Then, the non-active player add their events in the order of their choice. The non-active player's events will end up resolving first, since newly added events always interrupt what's already on the storyline. See the example below. It's my turn and I cast Apprentice Wizard to the surface of my Bottomless Pit. Also, my Bottomless Pit happens to be flooded and you have a Mariner's Curse there. The storyline starts like this: Summon Apprentice Wizard to the surface of Bottomless Pit There are no triggers yet, because the Wizard isn't the realm yet. So, we resolve the storyline and it looks like this: DONE: Summon Apprentice Wizard to the surface of Bottomless Pit Now, the Apprentice Wizard is in the realm, and we have three simultaneous triggers! As the active player, I declare mine first in the order of my choice. I order them like this: Apprentice Wizard Genesis (Draw a spell) Bottomless Pit ability (Kill Apprentice Wizard since it doesn't have Airborne) Then, as the non-active player, you declare your ability and add it ahead of mine. The storyline now looks like this: Mariner's Curse ability (Submerge Apprentice Wizard and return to hand) Apprentice Wizard Genesis (Draw a spell) Bottomless Pit ability (Kill Apprentice Wizard since it doesn't have Airborne) And then those three effects will resolve in order, yours first, then mine. See the 'Source is No Longer in the Realm' example below for more details.