The shadows created by nekros have different looks depending if you use the regular, irkalla or prime skins. However, no matter what skin I use now I can't get rid of the irkalla shadows (worst design imo, with huge flying pixel cubes coming out of them).
I recently noticed a player using the prime skin and irkalla helmet thus, resulting in having the prime Shadows. I tried the same combination and still got just the irkalla shadows.
For clarification:
Prime shadows looks like decomposing/decaying corpses.
Regular shadows looks like ghostly/ghastly bodies.
Irkalla shadows has huge horrible pixelated cubes coming out of them.