WARNING: The following contains major spoilers for Wizards: Tales of Arcadia, now available on Netflix.
While the first season of Wizards: Tales of Arcadia is the final chapter of the Tales of Arcadia series of shows, it isn't the end of the story, and it does plenty of the legwork to set up the finale: Trollhunters: Rise of the Titans. Rise of the Titans is an upcoming film that will serve as the conclusion to Trollhunters as well as Tales of Arcadia as a whole. It promises to unite "heroes from the hit series Trollhunters, 3Below and Wizards... in their most epic adventure yet where they must fight the Arcane Order for control over the magic that binds them all."
There's plenty about the new movie that's still unknown (including who these mysterious "titans" might be), but the events of Wizards shine plenty of light on where the story could go. "Control over the magic that binds them all" obviously refers to the Genesis Seals. While the vast bulk of the show deals with a time-travelling adventure to Camelot, the last few episodes introduce a new object to serve as a point of contention between the heroes of Arcadia and the Arcane Order: the Genesis Seals. The seals contain the essence of magic itself, and if broken, could result in a calamitous wave of magic that would sweep over the planet and destroy it.
These seals are a plot device introduced in Wizards in order to set up a threat for Rise of the Titans, as they seem to be of minimal importance in and of themselves. It's possible that their power over magic itself could prove relevant, but like the Ark of the Covenant in Indiana Jones or the briefcase in Pulp Fiction, it doesn't really matter what they do. Sure, they'll destroy the world, but given that Del Toro is unlikely to end his massive series with the world being, well, destroyed, they seem like a hollow promise. They are to be sought and chased after, and exist to give stakes to The Arcane Order's game of cat-and-mouse with the heroes of the film.
But who are The Arcane Order? Introduced in Wizards, they serve as partial antagonists for the show as well as a looming background threat. They are a triumvirate consisting of three members: Bellroc, Keeper of the Flame, Skrael of The North Wind and Nari of The Eternal Forest. They channel the powers of fire, ice and nature respectively, with all of them being proficient sorcerers older and more powerful than any other magic users seen on the show before. While Bellroc and Skrael seek the destruction of humanity as revenge for their mistreatment of the magic of the world, Nari has abandoned the Order's cause. She serves as an ally to Merlin, and later Douxie, for the events of Wizards, and will be crucial to the events of Rise of the Titans.
The Order acquired the Genesis Seals at the end of Wizards, but they can't unleash their power without all three of their members, including Nari. The final scene of the show featured Douxie and Nari hiding out in a city away from Arcadia. However, they were still being stalked by Bellroc, and a chase throughout the world seems likely. It's possible that such a threat might even require Douxie to call upon the help of the heroes of Trollhunters as well as 3Below.
While Wizards saw the return of the bulk of the Trollhunters cast, the characters from 3Below were largely overlooked with only a small part being played by one of its main characters, Krel. His sister, Aja, and their bodyguard, Varvatos Vex, both returned to their home planet, Akiridion-5, at the end of their series. Both aliens have been included in a list of characters appearing in the upcoming film, though, which means they could be returning to Earth.
A serious threat to the planet could see Krel call them back, as both he and Aja care about the planet deeply. While that's the most likely way for them to become involved in the story, there are other possibilities as well. After all, where better to hide Nari than somewhere the Order would never think to look -- beyond the furthest stars in the sky.
DreamWorks' Wizards: Tales of Arcadia stars Colin O'Donoghue as Douxie, Emile Hirsch as Jim, Lexi Medrano as Claire, Charlie Saxton as Toby, Steven Yeun as Steve, David Bradley as Merlin, Lena Headey as Morgana, Diego Luna as Krel and Kelsey Grammer as Blinky. It is available now on Netflix.