So you turned Shadolls into kind of an engine, interesting. I had the suspicion that it could be possible because once you drop an El-Shadoll the Fusion cycle basically sustains itself and relies less on the rest of the deck; also I was playing with the idea of finding a way for splashing Midrash on other decks, especially on those that can perform multiple Normal Summons (Shadoll Verz?). How about adding 1 Shadoll Dragon to the engine? The Flip effect, reusable through Falcon, provides control over monsters, while the second disrupts backrow. Lizard is an option too, but I think Dragon would be better for its ability of removing both monsters and S/Ts.
From your tests, which would you say is the best number of copies of "Shadoll Roots"?
On the Spirit Shadoll variant:
I have not tested it, but I don't see the appeal of "Creeping Darkness": Dedicating deck space to a searcher for Aratama/Lizard/Dragon doesn't look great when you could, let's say, run a 3rd copy of "Facing the Shadows" or Dealings for deck thinning, or perhaps apply Rabbit logic and try BLS; after all, with Aratama and Shadoll Fusion you should be able to put a LIGHT on the grave and set BLS up early game.
Haven't tried out Verz yet, I suppose it could be possible since Kerykeion benefits from dumping other Verz but the problem is that you can't go into it with the mindset that "Oh, they're DARK so it'll work like Constellarfacts." That's the main thing I see people doing wrong with the Shadoll engine; they treat it like the Artifact engine when the concept is entirely different.
Dragon is pretty legit as a one-of, I think I'll add it because getting Falcon from pitching Hedgehog is really lackluster. Pitching Beast for a free Upstart is nice too but Bujins do have potential to brick, and the other builds are relatively solid so I'll just add Dragon for now.
The number of Roots you should run depends on two things. First is the number of LIGHTs you have access to, and the second is how consistently you think you can thin the deck to reach Roots. I like having two copies because it kickstarts the engine without having to wait for my Midrash/Neph to get popped before I recycle Fusion. I also like having two copies because I enjoy having access to a different Neph target to pitch (if I already used Hedgehog/Falcon effects that turn) to recycle my Fusion, assuming I didn't use Roots to kickstart the engine in the first place. This'll probably change ever so slightly when I add 1 Dragon. I don't like to run 3 copies all that much, and I'll probably drop the third from the last two builds and replace them with that Dragon.
Creeping Darkness is integral to the Spirit build. Getting to your Aratamas is imperative to take advantage of the engine. The go-to combo is Ara into Niki into Fusion'd Neph to draw a card, trigger a Shadoll then pitch a Roots to recycle Fusion. Niki or Ara on the field against an Extra Deck card is an instant +3 off a Fusion in hand as well, and Creeping Darkness digs for Aratama. You never waste Creeping Darkness on Dragon or Lizard, you have other ways of searching those. If you get Aratama off a couple turns in a row, which is common because unless they're stupid the opponent will save removal for the Xyz play you telegraphed by putting Aratama on the board, you'll have Nikis padding your hand for a clutch R4 play down the line as well.