Merinir

Merinir the Black was a massive black dragon that lived during the Viking Era. It was so big "it's black wings overshadow the sun, casting night upon it's enemies: the mountains are no more than goblets of beer, the sky is his playground" according to Harkon Golden-Fist, who hunted down and slayed the beast at the cost of his life.

Appearance
Merinir was such a massive dragon, it was said to "overshadow the sun and bring night" by just opening it's wings. As a black dragon of immense size, it was big enough to "make the mountains look like goblets of beer" and "makes the sky his playground". The red eyes were like fire, and his claws were big enough to cut down a skyscraper. Such a big size was however Merinir's downfall, since Harkon Golden-Fist, a son of Odin active during the early Viking Era, was able to take advantage of it to take down the so-called Bane of Men.

Abilities and Powers
As a black dragon of such a big size, Merinir had an incalculable amount of physical strength. It's wings could create hurricanes, and it's fire was said to be powerful enough to melt rock and "bring Muspelheim to Midgard". It's unknown if Merinir had some other kind of magical power or ability that made him so big.

Trivia

 * It's big size proved to be Merinir's downfall, since one could easily take advantage of it. That was how Harkon was able to kill the dragon, though most of the battle is unknown.
 * Harkon believed Merinir could be the unknown enemy mentioned in the All-Father Prophecy.
 * It's possible Merinir's size was the result of a god's actions, what is believed by both Harkon, Odin and Tyr.