The Harbinger essentially disables your deck, which is such an interesting effect for a weakness. I've been trying to think of ways this card could be used to Norman's advantage.
The Rulings for Costs state that that:
An ability cannot initiate ... if the resolution of its effect will not change the game state."
If an effect that requires an additional cost would resolve, the additional cost must be paid at that time. If the additional cost cannot be paid, that aspect of the effect fails to resolve.
Which makes it pretty clear that while the harbinger is in play
Any ability that would have no effect without deck interaction cannot be activated
(You could not activate Word of Command—naming a Spell Card does not alter the game state)
Any cards with additional costs which interact with your deck cannot be activated
(You could not trigger an attached Bloodlust)
So we can only play cards that would interact with the deck if they have some other effect on the game and the deck interaction is not a cost of playing the card.
Survivor Discard Event Recursion
The first thing that sprang to mind was Winging It. If you have harbinger on the field, could you infinitely play this from the discard pile, so long as you can afford the resource cost?
Winging It does not exclusively interact with the deck. It starts an Investigate action.
The deciding factor on whether this is possible then, is whether the "If you do, shuffle it into your deck after resolving its effects." clause is an additional activation cost when you opt to play it from the discard pile.
"You owe me one!" has the same wording with no "after" timing. The card's effects are not dependent on drawing. You would still be able to play an ally's card if one or both Investigators are unable to draw. This event is still be playable.
Enchanted Blade is even more similarly worded: "you may spend 1 charge... If you do, you get +1 and deal +1 damage for this attack."
If something were preventing you from increasing your or damage, I believe you would be unable to spend a charge to empower the blade, as the game state would not change apart from paying a cost. If boosting only 1 of either the +1 or +1 damage was blocked though, there would still be an effect, the optional cost should be payable, and the empower effect activate-able.
Given these 2 cards, I'd rule that shuffling it into the discard pile is an effect that can't be resolved due to the Harbinger and the card can thus be played. Maybe I'm still mistaken and should just grim rule it though. Please let me know.
(This would also be applicable to Improvised Weapon and Impromptu Barrier, though I can't see Norman purchasing Versatile for either)
Discard Without Drawing
You could play Knowledge is Power to discard Spell or Tome assets from our hand without drawing. I struggle to see how it could be beneficial for Norman though.
We could also play Blood-Rite to discard cards without drawing. Might this be useful to discard a non-hidden weakness from your hand?
You may not optionally discard a weakness from your hand, but what if a weakness is the last card remaining in your hand? You have no choice of which card to discard, so if a discard happens, that weakness must be chosen. Blood-Rite's card effect could not resolve otherwise. The "Discard up to 2 cards" is optional though, so I think it would be unplayable here.
Are there any other noteworthy interactions? Perhaps level 0 cards for Versatile that I've overlooked?