If Black Uruks can discard Tentacles in the Water in the Water quest...

Dose that mean in Khaz you can use this treachery effect to discard Watchful Eyes?

No, couldn't do it -- the key word is "controls." You never control encounter cards unless the card specifically says you do. (Objective cards excepted -- you control Objective allies and attachments on your side of the table). "Hidden Threat" specifies that you have to control the attachment being discarded.

"Hidden Threat" specifies that you have to control the attachment being discarded.

ahh.. yup.. cool-e-o

So does that mean that if Hidden Threat is revealed during 'The Seventh Level', I would need to discard (or in this case, return to the staging area) the Book of Mazarbul?