WTF he's death!! Sewers SPOILER!

[dvow]

Somewhat big spoiler here. You know those weird pink organic things that keep spawning and following your progress? That's the 'shadow'. The monsters chasing you actually aren't spawned by the shadow, and the shadow doesn't like these monsters. That's what killed that monster. I think there's a spot in the sewers where the shadow actually kills a monster that was chasing you, but I was too busy hiding to see it.