Eidolon of Rhetoric

• WWizards of the Coast2014-04-26
  Official Ruling
  Eidolon of Rhetoric will look at the entire turn to see if a player has cast a spell yet that turn, even if Eidolon of Rhetoric wasn't on the battlefield when that spell was cast. Specifically, you can't cast Eidolon of Rhetoric and then cast another spell that turn.

Rulings via Scryfall