Necropolis?
No pile, so nowhere for it to return. In fact, the FAQ for Way of the Horse explicitly mentions it "The card returns to its pile, even if that is a non-Supply pile. A card with no pile, such as Necropolis (from Dark Ages), fails to return to its pile.", with similar wording for Way of the Butterfly
With Prizes, Tournament specifically uses the phrasing "gain any Prize (from the Prize pile)" thereby defining a "Prize pile" that they come from