This event takes place inside an underwater fissure. Down below, are a horde of monsters. The problem is, if you attack some of them, they don’t do anything, and just regenerate their health as if they are reset. If you stop attacking, they engage normally.
Also, not sure if this is a bug or just bad design, but in one instance where I attacked, something teleported me towards it, then I got teleported in again, and again. Each time deeper inside, in the midst of about 15 monsters. There was no chance to survive.