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.
While the harbinger is in play:
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Any ability that would have no effect without deck interaction cannot be activated [^1]
(You could not activate Word of Command—naming a Spell Card does not alter the game state)
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Any cards with additional costs which interact with your deck cannot be activated [^2]
(You could not trigger an attached Bloodlust)
We can only play cards that would interact with the deck if the deck interaction is not a cost of playing the card and they have some other effect on the game.
Improvised Event Recursion
The first thing that sprang to mind was Winging It. If you have harbinger on the field, you could infinitely play this from the discard pile, granting an endless 1 cost source of -1 Difficulty, +1 Clue Investigate actions!
(The reuse would also be applicable to Improvised Weapon and Impromptu Barrier, though I can't see Norman purchasing Versatile for either)
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.
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"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.
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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 argue that shuffling it into the discard pile is an unresolvable effect, due to the Harbinger, and that Winging It is thus playable.
Discard Without Drawing
We could play Blood-Rite to discard cards without drawing, or Knowledge is Power to discard Spell or Tome assets from our hand without drawing cards.
I struggle to see how it could be beneficial for Norman though.
Encounter Protection
Any Treachery that would interact with your deck simply doesn't.
This has limited usefulness in most scenarios, but can be of immense benefit in some specific campaigns. It's hilarious to draw encounter cards that just have no effect due to the deckless playstyle.
Cost Rulings
[^1]: An ability cannot initiate ... if the resolution of its effect will not change the game state.
[^2]: 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.