Jellyfish filled with the body fluid of drowning victims. Many of them gather around the harbor at dusk. Makes a sound like nails scratching glass.
They always appear in a group of four, they are really annoying if you only kill one or two, but using a group attack skill and they will all go down at once.
The Japanese name, Onibi (鬼火), is a term for a ghost light, known better in English as a Will-o'-the wisp, or Ignis Fatuus (Fool's Fire), among numerous other regional names.
Now believed to be caused by a chemical reaction of organic decay (which may also be found in marsh or swampland), or simple mistaken identity of fauna and natural bioluminescence - they were, in the past, ascribed to ghosts, devils, spirits and faeries, seeking to mislead travellers off the path to get lost, or possibly drown in the marsh.