Ghost Rat

It's part of the World Task A Pirate's Death to Me. Looks the same as a Rat.

They run very fast and make holes in lowest floor of the Spectral Ship.

Use a Ghost Duster on them. It will be helpful to use a Dwarven or Stealth Ring and Haste because they can make you drunk and they are very fast, but they are not immune to Invisibility. A Stealth Ring is preferable because they will not run away from you, making them easier to catch.