First some background information: in custom stories I greatly dislike dickmoves like sudden scares (people get scared of ANYTHING that's thrown at their face without warning, it doesn't matter is it a cute puppy or a mangled corpse) or impossible situations (like monsters appearing from everywhere at the same time and there's no way to discover the right route without dying a few times first.)
In my dream I was playing some custom story. I was in the game itself and I was sneaking around with a lantern, shitting bricks and swearing how miserable custom story it was. The monsters were spawning one after another, there wasn't any kind of silent creepy moments, story etc. there was just monsters and panic running. Plus they were able to crash through any obstacles, like even following through big, heavy doors they're not usually able to.
In addition they had created some mutated, bigger and uglier versions of grunts and brutes that were even stronger, faster and deadlier. So much that normal grunts and brutes didn't even scare me anymore. When seeing them I just thought "Oh they're just those lame first forms."
When I started to get along with the mutated versions and learned how to escape from them, the mod really started to piss me in the eye. A normal looking grunt spawned, but it was as powerful as the most powerful, mutated one. Obviously I couldn't see this, so I started to run towards the grunt and was about to dash and pass it fast and nicely. The uber fast and strong grunt then grabbed the poor me into a huge bear hug.
I died while cursing the maker of the custom story while "You have to go on..." text came to float to the screen.