Guillermo del Toro's Trollhunters expanding its universe with alien and wizard spin-offs https://t.co/jk164ecC1H— Entertainment Weekly (@EW) November 7, 2017
In the above sneak peek for season two, it's revealed to Toby that along with trolls, aliens and wizards are part of Arcadia. The Tales of Arcadia trilogy will share a mythology.
3 Below debuts in 2018 and will focus on two royal alien teenagers and their bodyguard. After escaping a coup on their home planet, they crash near Arcadia and decide to blend in as a Latino boy, a teen girl, and an elderly man.
Wizards will then debut in 2019 and unite all three of these mythological beings. They'll fight a battle that that will determine the fates of the troll kingdom, the aliens' world, and Earth.
Sources 1 and 2