How to Train Your Dragon: The Black Menace

Heather, daughter of Chief Stoic, leads the dragon riders in a confrontation against the Black Menace, a black blur of purple explosions and deadly whistling in the night sky.

Warning: there's violence (no blood, cause the shows don't do that, but broken bones, bruises, and just pain like soreness and maybe illness are involved); there's also trauma, ig?

(Oh, and if you wanted a better explanation for the plot, it's down at the bottom. But there's spoilers, so)

BTW, there won't really be any lore explanation for the HTTYD (How To Train Your Dragon) world, so if you're not familiar, I HIGHLY suggest you watch at least:
1 the first HTTYD movie
2 "To Heather or Not to Heather" in Dragons Race to the Edge (although I recommend watching the beginning of the show for better context)
3 you could also watch Riders/Defenders of Berk if you want more Heather backstory, but I didn't really need it

More detailed explanation:
Hiccup is now the mysterious dragon rider; Heather is the leader of the Dragon Riders and the daughter of Chief Stoic, but Hiccup is also Stoic's son/Heather's brother without knowing it; both characters still ride their original dragons (Toothless and Windshear), the riders are relatively the same personality-wise (aside from trauma-inducing traits and stuff), and finally, Hiccup and Toothless have more of a history with Dagur than Heather and Windshear originally had in the show... read to find out more.