Thread:Vorknkx/@comment-3547390-20120421171650/@comment-1496755-20120430102154

I remember one of the secrets in E2M3 opened (movable wall) when a certain Zombie was killed. Also, killing Chthon creates a bridge and opens the bar blocking the shaft to the exit :)

I can't remember if there are any movable walls that require several monsters to be killed ("X more to go", etc.), but hopefully I can make a playthrough soon and find out.