Can Defy counter a Hidden card when it's initially hidden, when it's cast normally, or when it's played from Hidden as a reaction?

Ruling: You cannot Defy a card when it is being hidden (it's not a spell being played at that point). You can Defy a hidden spell when it's played from Hidden as a reaction, as long as the printed costs meet Defy's requirements (4 energy or less and 1 rune or less). You cannot Defy non-spell hidden cards or hidden spells with printed costs exceeding Defy's limits.

Sequence:

• When hiding a card: Cannot be Defied (not playing a spell, doesn't go on stack)
• When playing from Hidden: Can be Defied only if it's a spell with printed cost ≤4 energy and ≤1 rune
• When casting normally (not from Hidden): Standard Defy rules apply based on printed cost

Nuances:

• Hidden cards are not public knowledge, so opponents don't know if they're spells or units when hidden
• Hiding a card is not considered "playing" a card
• The printed cost matters for Defy, not the 0 cost paid when playing from Hidden