I went solo on this level. Lot's of hidden places to hide and very dangerious.Was able to find all the skulls and place them correctly in place.
https://rumble.com/v1jfh74-zombie-army-trilogy-playthrough-solo-level-subway-to-hell.html
Alright! It was tough as I had a hunter alien on my heels the whole time, but I was able to reach Nicole, who was attached to the Marker. I defeated her (eventually) and made my escape with Ellie. What a cool game. Final boss and game ending! Great stream!