When a creature with Persist or Undying dies, you get to choose the order the triggers (Athreos and Undying/Persist) go on the stack. To get the Persist or Undying trigger to return it to the battlefield with certainty, you will have to place it on the stack second (top of the stack). That way it will resolve first, returning the creature. Then the opponent can ignore the Athreos trigger, since paying 3 life would be meaningless, as you can’t return the card from the graveyard to the hand if it’s no longer there!
If you stack the Athreos trigger first, then the opponent can choose not to pay 3 life so the card will return to your hand instead of to the battlefield. Then the Persist/Undying trigger can’t find the card in the graveyard and won’t do anything. On the other hand, if the opponent decides to pay 3 life to keep the card in the graveyard (instead of returning to your hand), the Persist/Undying trigger will then return it to the battlefield just afterwards. Seems like a difficult decision for the opponent to make!
Today’s Rules Tip written by Josh Stansfield