2. Using Surtur & Doing It Wrong
Although there has been no indication that Surtur will have any role in this film, there have been rumours that he could be presented as the mastermind behind Malekith's plans to send the universe in to darkness (kind of like how Thanos was the mastermind behind Loki leading the Chitauri in their invasion of Earth in the Avengers movie). If that's the case, he is one of the characters that Marvel must get right - he simply can't be massacred like the Mandarin was in Iron Man 3. Surtur has been anticipated for some time and there would be an enormous fan backlash if, for example, he was simply portrayed as a hidden malevolent presence or if he was changed in a similar way to how Galactus was changed in to a cloud in the Fantastic Four sequel. If the fire demon is to appear at the end (for example after the credits), it needs to be in his full comic book form, in all of his gigantic demonic glory.