Athreos triggers when any of its controller's creatures die, and no matter what they look like in the graveyard, they can still be returned unless 3 life is paid.
Tag: Athreos God of Passage
Athreos and Mutavault (or any animated non-creature).
If Mutavault is a creature when it dies, it will trigger Athreos and will be returned to your hand unless the opponent pays 3 life.
Athreos with Persist or Undying.
Athreos's trigger gets a little tricky when combined with triggers that try to return the card to the battlefield!
How Athreos interacts with tokens and with Rest in Peace.
Athreos can't return tokens that die, but the opponent can still choose to pay 3 life for no reason! Also, if a card doesn't actually hit the graveyard, Athreos can't trigger (e.g., with Rest in Peace).