Macall B. Polay/HBO Cersei Lannister and the skull of the dragon Balerion.
One of the biggest threats to Cersei right now is Daenerys Targaryen, who has a large army and three dragons. Dragons!
Unfortunately for Cersei, there's not much known about how to kill the magical, violent, and long-dead creatures.
But in episode two of season seven, Qyburn (who seems to serve every position on the Queen's council now), shows Cersei an invention that might work.
That weapon is put into action in episode four, "The Spoils of War." Bronn, fighting for the Lannisters, shoots Drogon with it. Although the dragon falls, he does not die. Will Qyburn's weapon eventually kill one of the dragons if aimed properly?
Although there's no proven and concrete way to kill a dragon, here are some of the ways that dragons could be killed, based on knowledge from the books and the show.