I know we had spoken about this topic in the past and the question about Zhaitan’s Shadow sphere has also been asked of Anet with unfortunately no response.
From what we have seen with the other dragons there seems to be a Primary Sphere of Influence and a secondary sphere of influence. The dragon’s primary sphere is quite evident because it shows up in their corruption as well as their physical make up. The secondary sphere of influence appears to not work in the physical realm and appears more meta physical.
Currently the Elder Dragons have shown mastery of the following sphere of influences.
Zhaitan: Death and Shadow, Mordremoth: Plant and Mind, Kralkatorrik: Crystal and Fury, Jormag: Ice and Persuasion, Primordus: Fire and Conflagration, Deep Sea Dragon: Possibly Water and who knows what.
Most of the secondary spheres seem self explanatory, except maybe Fury and Conflagration as we haven’t had a lot of examples. These Secondary Spheres really only seem to appear within the dragon themselves and don’t seem to be shared with its minions unlike the Primary Sphere. That being said once the Elder Dragon dies, the secondary sphere seems to be up for grabs for the other dragons and then can be shared among those dragon minions.
Zhaitan’s Shadow Sphere of Influence doesn't really appear in the game and when sifting through all the Risen pages on the GW2 wiki can I really see any Risen using any Shadow abilities, hence why I figured that the secondary domain is restricted just to the Dragon. When an Elder Dragon dies that magic is up for grabs. So I went to one of the first examples of one of these hybrid dragon minions that unknowingly appeared in the game with a new sphere of influence, the Shadow of the Dragon.
At the time of the release we did not know that the Dragons can consume their spheres of influence and push those influences onto their minions. With no clear example of Zhaitan’s Shadow influence, I looked at how the Shadow of the Dragon operated. When you fight the Shadow of the Dragon it spawns several different Shadow creatures, Shadow Tendrils, Malformed Shadows and Smothering Shadows. This appears to be clear evidence that Mordremoth consumed the Shadow influence from Zhaitan as well as the death spectrum. Mordremoth also creates Smothering Shadows in the final HoT story mission.
As you progress the encounter, Braham throws the divine fire to activate the areas around the makeshift jungle arena to eventually be able to damage the boss. The Smothering Shadows slowly walk toward the edges of the arena and Smother the divine fire and can only be harmed by it. The dragon minions also appear to fear and run from the divine fire and energy as well, as shown by the beginning of the Mystery cave.
After looking back at that fight, I started to wonder if Zhaitan was using the Shadow Influence to smother the divine energies of the God Temples and their statues in Orr and once the energy was smothered, use his mastery over death to use his Risen Priests and Priestesses of the Gods to corrupt the energy of the statues. I would imagine that Zhaitan would want to stop these Divine energies from scaring away his minions and would want to corrupt the essences to power himself even more.
The ability to stop the divine energy doesn’t seem to be an ability associated to the Death Spectrum, but it seems to be an ability shown by the Shadow Spectrum as shown by the Smothering Shadows. It should also be noted that taking back the statues themselves in Orr, certain pillars that have fire on them change their influence along with the associated god statues changing back to their typical god statue influence, Melandru’s statue growing back leaves for example. The Gods themselves also can’t be view by mortal eyes because of their divine light, which would make sense that Zhaitan would have negate this influence with the Shadow Sphere.