If you play Darius then a spell, but the spell gets countered by Defy, does that count as playing a second spell to trigger Darius?

Ruling: If a spell is countered by Defy, it does not count as a played spell for Darius's trigger. You would need to play another card after that, which would then be the "second spell" that triggers Darius.

Nuances:

• If you cannot pay the Defy cost, the spell is not countered and stays in your hand (it doesn't go to the trash), because Defy adds an additional cost to the spell rather than countering it after it's played.
• This interaction differs from reflexive trigger costs like Falling Star, where if you can't pay costs you must target someone else (including your own units) or whiff the trigger if no other viable targets exist.