Sundavrblaka, or The Beast, was a creature in the movie that was created by the Shade Durza with his dark magic. It was created from the dead bodies of Broddring Empire's Imperial Army soldiers that were set ablaze by Saphira during the Battle under Farthen Dûr. In the game, Durza created it with poison from his fingernail.
Sundavrblaka is present only in the movie, video game, and GBA game; in Eragon Durza is always on foot. On the Eragon movie production notes released by 20th Century Fox, Durza's steed is called "The Beast", or sometimes the "Cloud o' Fangs". In the GBA game it isn't present, but, however, it is mentioned while fighting Durza: "...she'll be too busy dealing with my Shadow wyrm anyway." Paolini later used the term Sundavrblaka for the shadow birds of Vroengard.
Sundavrblaka was a cloud of evil magic that resembled a large, black, eyeless dragon composed of smoke and ash. It lacked a solidly-defined body with only its head being solid. It is described as 'dark magic' by Saphira and as such it couldn't be damaged by weapons such as the sword Zar'roc. However, Saphira was able to bite the creature on the neck, causing the genderless beast some degree of pain.
The Battle under Farthen DûrEdit
Durza was seen riding this creature into the Battle under Farthen Dûr and during his fight with the Dragon Rider, Eragon, and Saphira, the dragon. After Eragon had launched himself towards Durza with her help, the steed continued to fight with Saphira. Sundavrblaka was solid enough to mortally wound the dragon: it bit her neck, punching through her dragon armor and piercing her neck scales. She was released when Eragon managed to stab The Beast in the neck. She fought with it until her injury forced her to crash-land away from the battle. Saphira nearly died from apparent blood loss, despite Eragon using magic to heal her. Sundavrblaka was presumed dead after Durza was killed by Eragon. Durza was heard saying the word "Sundavrblaka" in the spell to create it. Skulblaka means "Scale Flapper" and Lethrblaka means "Leather Flapper": the word "Sundavr" means shadow, so it is assumed he called it "Shadow flapper" to create a flying steed.