Jörmungandr

Jörmungandr (ヨルムンガンド) is a character introduced in Shinyaku Toaru Majutsu no Index. A member of GREMLIN, he is deployed to destroy the Russian bombing planes sent forth by the Anti-GREMLIN Alliance to spur Japan into action against GREMLIN during their invasion of Tokyo.

Etymology
In Norse mythology,, is a sea serpent, the middle child of the giantess Angrboða and Loki. He is so big that he is able to wrap himself around the entire world which gave him his other name as the Midgard Serpent, and is foretold that he will be killed by Thor who will in turn then die himself having been poisoned by the serpent's venom.

Appearance
He is simply described as a boy.

Lance of Gungnir Arc
He makes his appearance while assaulting a Russian tactical bomber. As he stands on one of their wings, before he can do anything, Stiyl Magnus' Innocentius appears before him. He grabs one of the rune cards that Stiyl uses and becomes intrigued on how he managed to set it up there without using magic as if it did it would also get shot down by magic. Stiyl communicates with him, saying that though he may think Innocentius is reliable and not interesting, Stiyl states that it is the same reason why it has no weaknesses. There, he challenges the boy to do as much as damage as he can to Innocentius.

The boy laughs, and tells Stiyl that just because he is not here doesn't mean he cannot be attacked. He tells of the legend of Jörmungandr on how it killed Thor with its poison. And thus the fight between them begins.

Poisonous breath
The original Jörmungandr used his poisonous breath as his greatest attack, able to kill even gods like Thor. Jörmungandr applies this in the form of a purple sphere of light which he can shoot with great speed and is apparently lethal. He shoots it down into the ocean, as if targeting Stiyl there.

Other Magic
Jörmungandr was able to not only reach an altitude of 10,000 meters, but also cling to a bomber, stand and jump around it as if on solid ground, and endure the extreme conditions there. He also apparently planned some sort of attack on the bomber by making his hands glow as if like a blowtorch.