(First post so forgive me if there are any issues or if this is worthless)
I found another… “skull” like shape in the beginning of the second mission (Blue Team), the same as the one found for the Ultra Banshee but I can’t figure out of there is a way to activate it or not. At the beginning of the mission, run straight. Go to the first window you see and look down. You can get to it from the outside area.
I think you’re talking about the Banshee Swarm Easter egg. That thing was found before the game even came out.