Hi guys, I'm the person that posted that video.
I'm open to everyones thoughts, I only made the post to see if it was already a thing I was missing and didn't know about or if we could work as a team to find out what it is.
Just to clear a few things up, I did not say that they could only be killed by their corresponding staff, I said that we killed each of them with the corresponding staff to see what would happen. Although, the ice zombie took about 10 blasts of the ice staff to kill, this is how we found it, it was left once the whole train was killed. Also, the theatre mode recordings cut out about 2 hours in, every single time. I don't think I have a single game longer than that in my theatre mode. I hope I don't get as much hate here as I did on that subreddit originally. I've been lurking here for a few days so I guess I should post an introduction then. If you guys have any questions about what I've been seeing then fire them my way, I want other people to see them and maybe get better footage so we can identify what they actually are.