Ixalan's Binding and Ashiok, Nightmare Muse
From a ruling on Gatherer:


  If there is no exiled card (perhaps because the exiled permanent was a
  token or was a commander that moved to the command zone in the
  Commander variant), Ixalan’s Binding won’t stop players from casting
  spells.


If you cast the card from exile using Ashiok then there is no more exiled card.  Therefore, your opponent can cast whatever they want, including Rampaging Baloths.