Guardians: Marvel Cinematic Universe
"Why have you called me?"
Not much is known about the being called The Erlking. He arrived in New York City in the chaos of the Battle of New York along with other members of the Guardians. He was previously known to Medusa in the parallel Earth she hails from, however he is not native to that Earth. Medusa reports that the Erlking had an extradimenional world of his own, and that he can apparently access that world from ours.
Medusa relates that she first encountered the Erlking in her world when their group was attempting to protect a famous paranormal romance author from the predations of a group of actual vampires. The Erlking, while not showing any particular care for the author, was hunting the vampires and assisted with the heroes’ infiltration of the vampire’s lair. He later appeared when Medusa showed signs of vampirism (having been bit), turned her into a large black dog, and then kidnapped her. It later was revealed that this was the Erlking’s peculiar method of preventing the progress of Medusa’s vampirism while her friends sought a cure.
He later showed up during what Medusa termed “our tour of some truly awful fanfic”, tagging along through several adventures as the heroine and her companions sought to escape the grip of the FanFic 5000’s more-than-virtual realities. This was probably why and how he came to our Earth—which has some disturbing implications.
The Erlking exhibited a number of powers during the Battle of New York. These included the ability to run in excess of 60 mph, to walk on air, and to grant both of these abilities to those around him. He also possesses a form of mind control, the ability to engender fear in his enemies by blowing a horn, and he caries a sword. Medusa reports that he can also travel to and from his home dimension, summon various servants from that world—typically a pack of large, black dogs, create various types of illusions, and he can also transform foes into one of his canine servants.