Summary
- Thrawn's alliance with the Nightsisters suggests he has brought a powerful army of undead Nightsisters to aid in his conquest of the galaxy.
- The Nightsisters possess dark magick and unique powers that even the Sith feared, making them a formidable threat to the New Republic.
- With the Jedi almost extinct, the New Republic lacks the defense to combat Thrawn's undead army, leaving Ezra Bridger as the only true Jedi to fight against hundreds of Nightsisters.
The Ahsoka finale set up Thrawn to replace the Sith as the next big Star Wars villain in-between the originals and the sequels. His return to the Star Wars galaxy bodes ill for the shaky semblance of peace the New Republic has created. Thrawn’s battle tact deftly defeated the Rebellion several times before, and now he promises to calmly and methodically return the Empire to its former glory. Rather than create a base on one of the city planets, such as Coruscant or Hosnian Prime, Thrawn is setting up his Empire on Dathomir. Moreover, what Thrawn brought with him from Peridea might be far worse than Thrawn himself.
While on Peridea, Thrawn created some sort of alliance with the Great Mothers of the Nightsisters. These mysterious witches possess countless spells and powers. And while it’s not clear whether they owe allegiance to Thrawn, both parties work together to escape Peridea and return to Dathomir. Despite Thrawn making it clear that escaping exile is his top priority, he allows the Great Mothers to unload hundreds of coffin-like capsules onto his ship before departing. In other words, Thrawn prioritized loading the capsules taken from the Nightsister’s catacombs over immediately leaving Peridea. Whatever is inside them could very well shape the next era of the Star Wars galaxy.
Your browser does not support the video tag. Evidence Suggests Thrawn Has Brought A Nightsister Army With Him To Dathomir 
While the contents of the Nightsister capsules has yet to be revealed, one popular theory suggests they are full of deceased Nightsisters. Given how the Nightsisters have the power to reanimate the dead, its likely the capsules on Thrawn’s ship contain an army of Nightsisters waiting to be awoken. The reason Thrawn risks Ahsoka, Sabine, and Ezra thwarting his escape from Peridea is because he wants the powerful army the capsules promise him. In other words, while he could certainly amass other ex-Imperials—such as the Imperials Shadow Council—to help him take on the New Republic, an instant army of undead Nightsisters is a much more efficient path to victory.
While the Ahsoka series was vague on how it happened, its clear Thrawn “awoke” the Great Mothers from their slumber. Similarly, the Great Mothers have the power to awaken their fallen sisters, who may possess unique and fearsome powers. Of course, this wouldn’t be the first time reanimated Nightsisters have appeared in Star Wars. Before the Nightsisters of Dathomir were wiped out, an ancient Nightsister named old Daka awoke an undead army to counter the Separatists during the Clone Wars.
Sith Were More Powerful Than Nightsisters – But Fewer In Number 
Traditionally, the Sith have been the biggest threat to the Republic for millennia due to their thirst for dominance and power. However, even the Sith feared the strange Force powers and magic of the Nightsisters. Due to Darth Bane’s Rule of Two, the Sith were always in lesser number than the Nightsisters. But because the Nightsisters never actually “died,” their numbers only ever grew. In the end, Count Dooku sent General Grievous to eradicate the Nightsisters on Dathomir, but Thrawn could very well have just brought them back.
If Thrawn’s capsules are full of Nightsisters, then the New Republic has a serious issue on their hands. The fact that the same characters show up again and again in the New Republic suggests there is a staffing issue. After over two decades of oppression from the Empire, no one wants to believe that Thrawn or the Imperials could ever return. Yet Thrawn’s instant Nightsister army could shatter the New Republic’s peace; the New Republic just doesn’t have the personnel to handle an undead army.
