Norse Mythology

Jörmungandr attacking Ships
Nidhogg Biting the roots of the World Tree
Fenrir being bound in chains by Tyr

Jörmungandr The World Serpent

Jörmungandr is a massive sea serpent that lives in the seas of Midgard or Earth, The World Serpent is the son of the god Loki and Angrboda, He is so large he wraps around the whole planet biting his own tail similar to that of an ouroboros. He is often associated with the beginning of Ragnarök (The end of the world) and Thor who he has had many battles with and ultimately fight each other to the death During Ragnarök. Because of this He is a large part of Norse Mythology.

Nidhogg The dragon

Nidhogg is a dragon in Norse mythology that bites at the roots of the World Tree Yggdrasil. He, Like Jörmungandr, is believed to play a part in Ragnarök as he is seen as an evil creature harming the World Tree which supports all the realms.

Fenrir

Fenrir is a massive wolf who like Jörmungandr is a son of the god Loki and Angrboda and is said to have a role in Ragnarök by killing Odin and setting the world on fire. Because of his role in Ragnarök he is bound by a magical chain and imprisoned, in doing so however the god Tyr had his hand bitten off by Fenrir.