Star Wars Jedi: Fallen Order - How Merrin's Nightsister Magic Works

screenrant.com:

Although they never make an appearance in the mainline films, supporting media like Star Wars Jedi: Fallen Order has developed the narrative of the planet Dathomir's Nightsisters and the powerful magic they wield. It is more commonly spelled «magick,» because it has very pagan and spiritual connotations in the way it is used by Nightsisters such as Fallen Order's Merrin. Dathomir's resident witches believe magick is a living entity, constantly surrounding them. This may sound quite similar to the Jedi Order's dogma as it pertains to the nature of the Force, and that is because Nightsister magick and the Force are practically one and the same.

The most famous character from Dathomir, Darth Maul, doesn't appear in Fallen Order, and even though he has a mastery of the Dark Side at this time, Maul has very little to do with the magick practiced by the Nightsisters. Use of magick on Dathomir is restricted to the Nightsisters, who rule over their male counterparts, the Nightbrothers. Maul left Dathomir to serve Darth Sidious as a child, but Nightbrothers are occasionally granted the use of Magick, as was the case with Maul's brother, Savage Opress. Nightsister magick taps into Dathomir's strong connection to the Dark Side, and can be manipulated to grant affinity to Nightbrothers like Savage, who have no prior experience in wielding it.

Related: What Fallen Order 2's Lightsaber Combat Can Learn From Jedi Academy

Although related, Nightsister magick usually manifests in different ways to how the Sith use the Dark Side. The strong presence of the Dark Side on Dathomir does result in powerful, more traditional Force users, though, as evidenced by Maul, Savage, and Asajj Ventress, who was cut from Battlefront 2. Merrin herself