Jörmungandr

Jörmungandr is a member of GREMLIN who first appears in Shinyaku Toaru Majutsu no Index Light Novel Volume 08.

Etymology
In Norse mythology,, is a sea serpent, the middle child of the giantess Angrboða and Loki, who is so big that he is able to wrap himself around the entire world.

Appearance
He is simply described as a boy.

Shinyaku Toaru Majutsu no Index
He makes his appearance while assaulting a Russian tactical bomber. He is then attacked by Stiyl Magnus' Innocentius, and 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.

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. He also apparently planned some sort of attack on the bomber by making his hands glow.