A Shadow Plasmoid is when a Progenitor becomes a plasmoid. They cannot be seen nor heard and are amongst the hardest to detect. However Taiidans have killed all Shadow Plasmoids due to their hand in creation of an alien species that would annilihate the galaxy that was far worse than the Manti. They created the Barsen.
The only way to see a Shadow Plasmoid is to have it in a cloak even then its near impossible to see their face without being close up. How they became per say evil plasmoids is by their creations. They are powerful but are entirely different than the Plasmoids of the Coragudans. These plasmoids have shown great interst in creations of mass destruction and species that are too dangerous to be around. They however are all dead due to the Taiidans ripping them apart as the Taiidans with thier implants can see them as for nearly a millenia the Shadow Plasmoids would lead them. The image depicted is a shadow Plasmoid through the Eyes of Dvr.
Asti the Fallen brought the Shadow Plasmoids back but to become his army. They have implant his ideas in peoples heads and he gave them the power to take what they wish. The Shadow Plasmoids were seen throughout Earths History as Demons minor gods and were helped an evil from the 20th century to eradicate an entirebpeople. The shadow plasmoids however have gone back in time multiple times and change events.