The story in "Burning Midnight" is relevant to the second graphic novel in the trilogy of post-How to Train Your Dragon 2 comics. This second installment in the new trilogy is known as Dragonvine.
The Dragon Riders share stories in Stoick's memory after they become sealed in a cave while escaping from a dangerous new species of dragon.
This comic follows the Dragon Riders, plus Valka and Eret, the most recent added members of the group. After Toothless collapses a cave entrance, sealing the group inside, they share stories in Stoick's memory settings around a fire as they plan their next move.
Since "Burning Midnight" was released on Free Comic Book Day, you can read it in high quality for free by following this link if you have a Dark Horse Comics Account.
There is a small discrepancy between "Burning Midnight" and the original film, Gobber states that his arm and leg were taken by the same Monstrous Nightmare, while in How to Train Your Dragon he states that it was two different dragons.
Though it may be possible that the latter was exaggerated for the purpose of impressing the teens.