Perhaps the most malevolent of the Shetland monsters. It is briefly but vividly described by Jessie Saxby in Shetland Traditional Lore (Chapter 9):

The Marool was a sea-devil who took the form of a fish, and was a very malignant creature. He had a crest of flickering flame, and eyes all over his head. He often appeared in the centre of mareel — that is seafoam when it is phosphorescent. He delighted in storm, and was heard to shout his wild exultant song when some luckless bark went under.

[Motif: G308]