During the speculation of who will be the villains of Thor: The Dark World classic names such as Malekith, Sutur and Ulik The Rock Troll. Dark elves Malekith and Kurse/Algrim being the confirmed villains of the film, it had been originally assumed they would be it. Recent rumors point that the all the realms will be explored including the addition of Surtur and Hela. However, the title The Dark World seemingly gives the impression could feature more villainous creatures from other realms.
Over the summer/fall set photos of the film had been rolling out with images of Thor, Sif and Fandral fighting a group of marauders and creatures. Everyone had assumed these were dark elves. However, with the new look at Malekith's (Eccelson) face we have an idea of what the elves will look like. They look slightly more human than the creatures from set photos along with different costumes. So who are these creatures, Surtur's army, rock trolls or possibly the undead?
Another possibility could be villainess Hela. Actress Alison Krige best known as Star Trek's Borg Queen had confirmed an unnamed role in the sequel. Many had assumed it would be the dark elf Queen but another option could be Hela. The villain wants to rule more than just the realm of Hel and invades Valhalla the realm of fallen heroes. She's originally the daughter of Loki but she might be changed to mother to fit the films better. If you look closely at Hela's army from recent comics they sort of look like the group of baddies facing off with Thor. There had been rumors that Fandral will be killed off and this aspect would give reason for the group to travel to Valhalla to perhaps bring him back. During this resurrection rescue Hela could be pushing for a full scale invasion of the realm.