An account

I was with two characters, people I knew were fictional. Something happened (a guy "died" and fell into a "coffin" filled with liquid concrete in a doorway?) and the characters took it seriously. However, I knew it was not real and wanted to show them. I dig out the concrete, showing them the person who fell was just a cardboard cutout. Suddenly the atmosphere of the "scene" changes. I get scared. The two characters 'freeze', and their eyes turn black. They say I should not have done that. Their next few sentences make some sense, but then I realize they are talking <PERSON> gibberish. I suddenly "know" they will soon shapeshift into horrific abominations, so I flee. I run through a corridor to the front door, but it is locked. I had no choice but to navigate the many corridors of the "mansion" I was now in, and avoid the monsters stalking them. At some point I was attacked by an older lady, also talking gibberish. I could barely push her off of me.