Athreos brings up so many questions, it needs to be broken out into multiple days to avoid overwhelming you with walls of text!
Another common question is what happens when your Mutavault (or some kind of Keyrune, perhaps) dies while it’s a creature and you control Athreos. The animation effect ends when it hits the graveyard, right? So how can Athreos return a creature if it’s no longer one? Well the answer lies in the nature of “leaves-the-battlefield” triggers, which look back to just before an event to see if anything should have triggered from an event. Since Mutavault was a creature when it died, Athreos triggers for that event. Then it can continue to track that card across the zone change that was expected, and will find the Mutavault card in the graveyard to return it to your hand!
Today’s Rules Tip written by Josh Stansfield