Can I reveal a hidden unit (like Teemo) during my turn and play it at a different battlefield than where it was hidden?

Ruling: Hidden cards can only be played at, or affect units at, the battlefield where they were hidden. You cannot reveal a hidden unit and play it at a different battlefield, even if you control that battlefield.

Nuances:

• This rule applies to all hidden cards, including cards that create spirits or other units
• The FAQ on hidden clarifies this restriction