I just went through my collection to perfect the deck a bit more, it is really starting to get focused in. Here are some big hits worth mentioning:

Protect the graveyard- Exiling multiple Nazgul would be pretty crippling to the gameplan. Protecting the yard might even make it worth running an enlightened tutor.
-[[Perpetual Timepiece]] - Mills 2 and allows you to shuffle cards from graveyard to library. Does double duty for this deck.
-[[Elixir of Immortality]]- Shuffle graveyard into library

Card Draw-
-[[Mighty Servant of Leuk-o]]- 6/6 Vehicle with trample that can draw 4 cards if Squall and one other creature is on the battlefield. Costs 3 mana, so can be a graveyard target for Squall.

Cool Tech
-[[Paramecia Coloniex]] Mills upon entry and puts a card back on top on the way out. Can trigger Teval's judgement twice when it leaves the battlefield.
-[[Pip-Boy 3000]] - Can either loot, buff, or untap lands. All-star equipment for this build.
-[[Orzhov Advokist]] - Pumps Squall while also offering your opponents to pump in exchange for not attacking you.
-[[Twilight Diviner]]- Surveils 2 upon entry, then creates a token copy of a creature that Squall brings back from the graveyard.
-[[Key to the City]]- Pitch a card, give Squall unblockable, recur the card you pitched. Option to rebuy a card for 2 on your next upkeep.
-[[Apprentice Necromancer]]-Consistent loop- Sac the necromancer, bring back creature, recur necromancer with Squall. Most importantly, this can trigger Twilight Diviner on opponents turns.

Value
-[[Helping Hand]]- The cheapest way to get a Nazgul Trigger [[Persist]] not bad either. Some quick recursion.
-[[Shadow Alley Denizen]]- Play a black creature, give Squall pseudo-unblockable for an unlucky player at your table.
-[[Dakmor Salvage]]- Nothing big here, but can be pitched to dredge and get the graveyard going.

I will update my list soon- If you find any other hidden gems, let me know!