There are not many legends about seatroll (but is a character who often appears in folktales).
It is described as a creature with multiple heads that lived in the sea. It could help you in distress, but then you had to sacrifice a child in return.
Skroemt is probably a generic term for several unexplained phenomena, the legends usually describes it with hideous sounds.
There are some few descriptions: a wandering ghostly white woman, a blue goat which changed form and turned into a pig with long ears, a headless man, a terrible beast with fire in his mouth, a pastor’s dead wife coming back etc.
Skurekallen (sort of a grain spirit)
Skurekallen (grain spirit) was an old man associated with a certain fear. It was about not being the last harvest the grain. If this was the matter you had to accommodate skurekallen through the winter.
And what could be even worse, was that they had to sacrifice themselves and in this continue a life as a grain spirit, in order to ensure the existence of this character.