Can Ornn Legend's generic power be used to pay the hidden cost of gear cards like Zhonya's Hourglass (similar to using Kai'Sa Legend for spells)?

Ruling: No, you cannot use Ornn Legend (or Kai'Sa Legend) to pay hidden costs. Hiding cards is not the same as playing them, and these legends only generate power for playing cards of their respective types.

Nuances:

• Hidden is not an ability keyword like deflect or ganking
• Hidden effects are never active "on the board" and don't require declaring usage
• It would be illogical to reveal a card you're about to hide just to check legality