Encounter set:
Shadow and Flame
Shadow.
When Revealed:
Attach Counter-spell to Durin's Bane. (Counts as a Condition attachment with the text: "Forced: When a player plays an event, discard the top card of the encounter deck. If that card is a treachery card, cancel the effects of the event, discard the event player's hand, and discard Counter-spell from play.")