Response: Cancel a shadow effect just triggered during combat.

'The hasty stroke goes oft astray,' said Aragorn. 'We must press our Enemy, and no longer wait on him for the next move.'
–The Return of the King

Attach to a hero. Attached hero gets -1

Response: Exhaust Dark Knowledge to look at 1 shadow card that was just dealt to an enemy attacking you.

'Go on then!' said Frodo. 'What do you know?'
'Too much; too many dark things,' said Strider grimly.
–The Fellowship of the Ring