It was so far over the line that it got emergency-banned in Standard and is banned in a bunch of formats because it basically warps games around itself
This functions more as top-end for an artifact stax deck than a stax piece itself, but it can lock down an opponent youre worried will disrupt you and draw a bunch of cards
Even in a 40 life format (*cough* Commander *cough*), Athreos tends to be a great long-game clock that also nets you good stuff here and there, at least in the early game
You can simply treat it as a standard single-effect enchantment or a reusable sorcery, never having to bother with its transformation requirement ever
This card works very well in Commander decks that dont let the mana empty from the mana pool, like Kruphix, God of Horizons, or cards that let you untap your permanents, like Seedborn Muse or Wilderness Reclamation