Can hidden cards be played directly to battlefields, and where can hidden cards be played from?

Ruling: Hidden cards can only be played at Battlefields you control, not at your own base. If you play a hidden card at a Battlefield you control, you have to wait until your opponent's turn to be able to play them.

Nuances:

• Hidden cards must be placed facedown at a Battlefield you control
• You cannot play hidden cards to your own base
• Playing hidden cards at Battlefields you control allows you to avoid paying their normal energy/power cost