History
The Shadow Nixes are mystical creatures that feed off electrical currents, and are native of Vanaheim. The Vanir had to get rid of electrical instruments in order to fight off the presence of these creatures in their realm, after they almost destroyed it. The Vanir used a "Great Light" located on top of their village to keep the Shadow Nixes at bay.
After using an Asgardian rune stone, Avengers Hawkeye and Falcon were accidentally teleported to Vanaheim, at a time when the "Great Light" went out, and the Vanir couldn't reignite it as they didn't understand the potions required to do so. As the Vanir and Hawkeye fended off the Shadow Nixes trying to get into the village, Falcon managed to create the "Great Light," as the potions needed to create it were nothing more than chemicals. As the Great Light was reignited, all the Shadow Nixes in the area of the village were destroyed by its exposure.
Two Shadow Nixes had been transported to Earth during the same event that had brought Hawkeye and Falcon, and the Avengers tried to stop them from feeding off New York's electricity. When Thor reactivated the rune stone and brought Falcon and Hawkeye back, the God of Thunder used a spare amount of the chemical that produced the "Great Light" to destroy them.[1]