Fun meme, I can see it being played by Wowhobbs but not anywhere else.

It's like a worse Twilight Guardian. I don't see it being played over Bone Wraith or any other mid-game neutral taunt.

Obviously a meme, but not a playable one

Very strong board control tool, nice art, cool flavour, seems reasonably balanced. I like it.

While I like the idea of the deck, I have a few things which I think make it weaker than it could be.

1. Too many singletons. This decreases the consistency of the deck. It might be worth it if you want to play Zephrys and DQA, but they aren't even in the deck.
2. Betrug without Plot Twist. An 8 mana 5/7 simply isn't worth it if you only cheat out 1 minion with it at the most, especially considering there are only like 3 cards in the deck with real synergy with it (Deathrattles).
3. Jaraxxus is simply too slow in the current meta.
4. Sathrovarr is just too slow, since you can't combo it with anything in the same turn in this deck. He would make more sense in a Quest Warlock deck.
5. Spirit Jailer has very bad anti-synergy with Archwitch Willow. One of the two has to go. If you want to play a small demon, Mo'Arg Artificer is way more important to a control warlock gameplan than Spirit Jailer.
6. Weird tech cards. Bad Luck Albatross, Acidic Swamp Ooze and Twisted Knowledge may all have their place in a control warlock list, but not in the same one. You'd put one of those in to improve a specific match-up in the meta.
7. Imprisoned Scrap Imp is not worth it in a deck consisting of mostly good minions. You'd want it with tons of small minions, since a 1/1 going to 3/2 is a way bigger improvement than a 4/6 going to 6/7.

Using the points above, I made the following decklist:

This uses your deck as a basis, but makes it more consistent, removes some weird card choices and adds a dragon package for both survival and better Vectus target in Plagued Protodrake.

I think that depends on the meta. She could fit, but with Plot Twist we have a large chance of pulling all the Soul Fragments out of our deck leaving her with only a few rushing souls. She could be nice in a slower meta though, as another big board-in-a-card. Kragg is better in a more aggressive meta.

The Soul Fragment package is more here to support the deck and to help the quest along than the focus of the deck. The 5 mana demon is strong, but it's terrible to get off Archwitch Willow and isn't really better than Abyssal Summoner.

Kanrethad Ebonlocke could work, but the second half has some anti-synergy with Archwitch Willow. You could consider cutting 1 Siegebreaker for him.

You're also greatly underestimating how good Lorekeeper Polkelt will act in this deck, since he actually directly counters your other points. You play him after you finish the quest, putting all your Soul Fragments on the bottom of your deck as to not accidentally grab them with your hero power. At this point you'll be able to stabilise with your big taunts and free cards, so you won't need to shuffle Soul Fragments into your deck anymore. The point also isn't to add a 4/5 to the Archwitch Willow board, but to double your chances of drawing her.

The point of the quest is to counteract the heavy curve of this deck. Because of the big demon package, we want to have a chance to play them for free. You could make a Soul Fragment/Big Demon deck, but that would just be a completely different deck from this one. I look forward to seeing your spin on that archetype though.

This is a good card in a dedicated Soul Fragment deck, but unlike many of the other Soul Fragment cards it's unplayable outside of that. This scales directly with the amount of soul fragments in your deck, and I don't really see people having that many of them in their deck since one of the best things you can do with them is destroy them.

I really love this card. It thematically perfectly blends the two classes, it mechanically helps a strategy they both like to use, it's strong, it's skilltesting (is the overload worth the rush?) and the art of the tokens looks really cool.

Very unique card, I can see it being put in Highlander Mage but not as a stand-out card

I don't see much use for this card, but i'm sure some genius deckbuilder will think of something brilliant with it

Great card in Libram paladin, and already worth it with 1 discount

1 mana 1/3s with upside always see play, and so will this one.

Like School Spirits, it's removal and healing in one. Great combination, will see play in any control warlock.

Great control card, both removal and healing in one. Will see play in all control warlock decks.

Good card, tempo plays are always nice. Will see play in most soul fragment decks.

Pretty good in a control warlock, but not sure if it's worth running over Abyssal Summoner. Maybe alongside it.

Overpowered card. This will carry tempo mage for the next year.

If control DH will be a deck, it will be because of this card. It's like a better Duskbreaker, which was insane.

It's like a Truesilver Champion with additional upside, great card. also curves straight into Glaivebound Adept.