So, Thor: Ragnarok has Hela and Fenris-wolf, who are both Loki’s children in mythology, if not in the Marvel mythos, and who play a role in mythological Ragnarok.
Absent, however, of Loki’s mythological brood and the monsters of Ragnarok is Jormungand, the world-serpent – who in mythology, kills Thor in Ragnarok by piercing him with its fang.
Now, obviously Thor doesn’t die in the film and doesn’t battle with the world-serpent.
But–
He does get pierced by a snake.
Specifically, a stabby little shit of one who goes “Mblergh, it’s me!”