The Nihil and Drengir proceed the Return of The Sith as Villains could make appearances

there factions that preceded during The Golden Age of The Jedi during the High Republic

-The Nihl are akin to Enfys Nest and Cloud Riders from Solo: A Star Wars Story those less principled lead by Marchion Ro.

-The Drengir are similar to the Gravemind and The Flood lead by The Great Progenitor.

They could make appearances in earlier episodes also its great to see Star Wars villains be more than Darksiders or Military Armys.