There are many creatures that appear in the Norse Tales, Sagas and Myths from Wights to Wyrms and even great Sea Monsters. Some are worshipped and some are feared. These are all mentioned below, but keep in mind these are creatures and there are many animals also feared and worshipped it the Norse realms.
First are the Vaettr or “Wights,” these are spirits mainly attributed to nature and act as guardians and even teachers. Each race has its own Vaettr, which then divide further into Families or Aettir. There are also many different types of Vaettr. Sjovaettr are wights of the sea, Vatnvaettr are wights of freshwater and rivers, Husvaettr are house wights and the most well known of these are the Landvaettr or wights of the land. These wights promote flourishing in the land and then protect it. Iceland has four Landvaettr that each guard a cardinal point of the country. All appear on the Icelandic coat of arms and the Krona coin. The first is Dreki a great dragon of the east quarter. The second is Gammur the eagle of the northern quarter. The third is Gridungr the bull of the western quarter and the fourth is the Jotun Bergrisi of the southern quarter.
"According to the Saga of King Olaf Tryggvason in Heimskringla, King Harald Bluetooth Gormsson of Denmark, intending to invade Iceland, had a wizard send his spirit out in the form of a whale to scout it out for points of vulnerability. Swimming westwards around the northern coast, the wizard saw that all the hillsides and hollows were full of landvættir, "some large and some small." He swam up Vopnafjörður, intending to go ashore, but a great dragon came flying down the valley toward him, followed by many snakes, insects, and lizards, all spitting poison at him. So he went back and continued around the coast westward to Eyjafjörður, where he again swam inland. This time he was met by a great bird, so big that its wings touched the hillsides on either side, with many other birds large and small following it. Retreating again and continuing west and south, he swam into Breiðafjörður. There he was met by a huge bull, bellowing horribly, with many landvættir following it. He retreated again, continued south around Reykjanes, and tried to come ashore at Vikarsskeið, but there he encountered a mountain giant (bergrisi), his head higher than the hill-tops, with an iron staff in his hand and followed by many other giants (Jotnar). He continued along the south coast but saw nowhere else where a long ship could put in, "nothing but sands and wasteland and high waves crashing on the shore."- Wikipedia Extract.
Disir or “Lady” are female spirits in Norse lore associated with being spirits of dead female ancestors. They are similar to that of the Vaettr in nature but can be benevolent or antagonistic towards mortals. They are often linked to fate.In Norway and Iceland, this festival was known as the dísablót, “sacrifice to the Disir,” and took place at the beginning of winter. It could be held in either a private house or a formal temple, and from the name of the festival, we can conclude that a sacrifice was its principal ritual act, and literary sources add that a lavish feast was another central part of the event.
Vordr or “Wardens” are guardian spirits otherwise known as a wraith. They dwell beneath the roots of a families Vardtrad or “Warden tree,” situated in the yard. Usually a linden, ash or elm tree. At times, the warden could reveal itself as a small light or as the shape (hamr) of the person. The perception of another person's warden could cause a physical sensation such as an itching hand or nose, as a foreboding or an apparition. The warden could arrive before the actual person, which someone endowed with fine senses might perceive. The warden of a dead person could also become a revenant, haunting particular spots or individuals.
Next we must speak of the Draugr or revenant. These are reanimated corpses which become guardians of their own treasure that was buried with them. They possess unnatural strength and devour their victims. Animals that graze near a draugr’s grave are said to be driven mad. They are described as being Hel-Blar or death blue and alternatively Nar-Folr or corpse pale. They are said to be created by being either buried not horizontally or by in life being mean or greedy. A similar creature is that of the Haugbui or Mound dweller these are pretty much exactly the same as a draugr but are unable to leave the gravesite.
“The will appears to be strong, strong enough to draw the hugr [animate will] back to one's body. These reanimated individuals were known as draugar. However, though the dead might live again, they could also die again. Draugar die a "second death" as Chester Gould calls it, when their bodies decay, are burned, dismembered or otherwise destroyed.”- The function of the living dead in medieval Norse and Celtic literature by Gregg A Smith
We cant talk Norse creature without including the Troll. Trolls are beings which dwell in isolated areas such as mountains and caves. They are rarely helpful to humans and live in small groups or families. Numerous tales are recorded about trolls in which they are frequently described as being extremely old, very strong, but slow and dim-witted, and are at times described as man-eaters and as turning to stone upon contact with sunlight. A Scandinavian folk belief that lightning frightens away trolls and Jotnar appears in numerous Scandinavian folk tales, and may be a late reflection of the god Thor's role in fighting such beings. In connection, the lack of trolls and Jotnar in modern Scandinavia is sometimes explained as a result of the accuracy and efficiency of the lightning strokes. The English family name Trollope is derived from the place-name Troughburn, in Northumberland, England, originally Trolhop, Norse for "troll valley".
Sea monsters are also present in the Norse sagas, the first is Lyngbakr or “leather back” a huge whale like creature living in the Greenland seas which poses as a heather covered island to lure in seafarers, and when they land on it ,it submerges killing all upon it. The next is Hafgufa or “Sea Steam” similar to that of Lyngbakr it disguises itself as a pair of rocks rising from the sea and devours all including whales, ships and men. It is described as the mother of all sea monsters.
“As Örvar-Oddr and his crew were sailing southwesterly through the Greenland Sea, the deck officer Vignir knew this area would be dangerous, and made Oddr agree to sail the ship beginning the next day, to which Oddr requested Vignir advise him. As they sailed, they spotted two rocks which rose out of the water. The presence of these rocks puzzled Oddr. Later, they passed by a large island covered in heather. Curious, Oddr made up his mind to turn back and send five men to check out the island, but as they approached where the island had been before, they saw that it and the two rocks vanished. Vignir explained to Oddr that, had they landed sooner, the crew would have surely drowned. The "rocks" and "island" must have been two sea monsters—Lyngbakr, the greatest whale in the world, and Hafgufa, who bore all the monsters in the sea. The rocks had surely been the nose of Hafgufa; the island, Lyngbakr; Ögmundar Eyþjófsbana had summoned the beasts to kill Oddr and his men.”- Wikipedia extract.
Marmennill or “Mermen” and their female counterparts Margygur or “Mermaid,” are skilled in the art of prophecy and live in the ocean depths. Little else is known of these creatures.
Although Wyrms and serpents are also classed as Norse creatures I will go more in depth with these on their own articles.