/u/ItsAllFolklore and I have had some interesting discussions in the past about giants and how they figure as both literary devices in poems such as The Ruin and as real folkloric creatures within the Anglo-Saxon popular mythos.

One type of creature who does seem to have persisted in popular consciousness throughout the period is what we might term today the "fae folk" - that is to say elves, goblins and the like. Elves are a relatively common occurence in Anglo-Saxon culture; they don't appear in 'historical' sources like The Anglo-Saxon Chronicle but appear as elements in names and toponymns, and also appear in scientific and medical texts. Elves don't appear to have been considered inherently malignant - names such as Ælfwyn and Ælfræd imply that they were considered both beautiful and wise - but they could be dangerous if crossed or provoked. The easiest way to avoid this, of course, was to avoid areas where they were known to inhabit. The 9th Century medical textbook known as Bald's Leechbook includes, alongside cures for infections and cirrhosis and various 'real' maladies and ailments, a section on cures for 'elf magic' typically occurring in the forms of curses on animals. The cures for these often include prayers, as well as the leaving of gifts out for the elves in the hope that they will be mollified into lifting their curses.

/u/BRIStoneman does a good job touching on many of the subjects here. We must keep in mind that people take their beliefs - the foundation of their folklore - very seriously. The monsters and terrifying entities of Anglo-Saxon tradition were not nursery rhymes and boogeymen invented to terrorize children.

Most of the literature points toward fear of revenants (walking corpses), elves (in their various forms and names), and devil-associated demons. Although the Anglo-Saxon world included traditions involving giants and dragons (and other fabulous beats) these were generally thought to belong to times and/or places removed from the present world, so although our Anglo-Saxon peasant likely believed in them, he feared them less because they were not likely to affect him personally.

Archaeology is revealing a rich tradition of corpse mutilation, presumably to prevent corpses held in suspect from being able to walk or talk. Precautions include shoving large rocks into the mouths of the dead or decapitation with the heads placed at the feet of the corpse - always good ideas if one has any doubt about the ill-intent of a corpse!

As /u/BRIStoneman, points out, Anglo-Saxon medical texts include many ways to avert curses and the ill-intent of elves: although the modern world conceives of them as cute and relegates them to the role of the "elf on the shelf," they were real and terrifying in Northern Europe in pre-modern times. Anglo-Saxon texts capture and/or allude to this terror: these supernatural beings were fickle, easily offended, and quick to respond with deadly or life-changing effect. They also coveted human captives frequently abducting infants and handsome young people. They were not to be trifled with, and they were taken very seriously.