Can Hidden Blade hidden at Battlefield A target a unit at Battlefield B?

Ruling: Hidden Blade cannot target units at a different battlefield. Hidden cards can only affect units that are at the battlefield they are hidden at.

Nuances:

• The targeting restriction applies to the battlefield the hidden was revealed from
• Any units played by the hidden effect must be played to that battlefield
• Non-targeting effects from hidden cards are not restricted to the same battlefield
• If both the target and the hidden card move to a different battlefield before the effect resolves, the target would still be illegal (unlike effects with the word "here")