After the Hidden World was found and saved in Berk, the Dragon Crew have become it's sole guardians along with Toothless's new Light Fury mate. But Grimmel is far from over. Grimmel, being alive, found himself in allience with the Dragon Hunter reminants that are long without Viggo and Ryker in the events of the Netflix Series (Though Certain Elements of Season Five, like how Drago had his Bewilderbeast, has to be considered non-canon cause of the origin flashback from Night of the Night Furies being a great contridiction, and the gaining of the Bewilderbeast egg is now to be considered a new chance for a new Bewilderbeast for Valka's dragon sanctuary, amongst other details) now under the leadership of a deluded madman, Wackattack the Wacko, a crazy and insane loonitic that wants all the dragons to himself because that would make him worthy to become a norse god, and all three villain teams, as the groups are now hunting for a legendary super-dragon bigger then both Red Deaths and Bewilderbeasts combined: The Histaurus, (Like this), often discriped to be the Odin of Dragons for it's power to control and travel in time and it's inability to die as it is said to be the primordial spieces where all dragons assended from, has it can change it's ability of fire to water or other abilities depending on it's current resting place. It's wings are able to splice into reality and into the timestream and swim in it like water. However, it is a creature that is heavily guarded by a sub-spieces dragons that take the form of all known dragon spieces, refered to as The Primoridals, the links between the Histaurus and all other Dragon spieces. To the Lougers, if Grimmal and the other villains gain control of Histaurus, they can control the Primoridals by extention, and create off-shoot corrupted versons of all known dragon spieces to control for their own means, along with a more greater risk of Grimmel having control of all of time, and would allow him to make any change he would want in all of time. But to Hiccup, he ended up seeing Histaurus as a chance to bring Stoick back by preventing Drago Bludfist from ever occuring as he was by stopping the dragon attack that made him as he was and prevent some events of the second movie from occuring apart from finding his mother, but the concerned Lougers and the rest of the dragon crew, knowing the risks of time travel always brings, need to find a way to get Hiccup to not take the kind of oppertunity a time traveling super-dragon would offer and focus more on saving it from Grimmel, but can Hiccup resist ANY chance to have Stoick back?
PTE Redux Status: Not entirely unworthy, as there are several ideas concerning continuing the Dragon Riders' adventures in the PTE after The Hidden World.