While fans of the X-Men might be more familiar with the Brotherhood of Evil Mutants that was first organized by Magneto, there is also another group of mutants known as the Sisterhood of Mutants that formed during the Utopia-era of the X-Men by the returned evil of Madelyne Pryor.
The Sisterhood has little relation to the Brotherhood beyond the similar names. While the Brotherhood allowed mutants of all genders, the Sisterhood exclusively featured female members. The group saw a number of incredibly powerful mutants (and Asgardians) join since their debut, but which member of the Sisterhood of Mutants was the most powerful?
10 Lady Masterminds
Jason Wyngarde was the first Mastermind and original member of the Brotherhood of Evil Mutants, though after his death his mutant daughters Regan and Martinique each claimed his name as their own.
Regan goes by Lady Mastermind and her illusions have a hypnotic element that can create physical reactions in her victims, while Martinique/Mastermind's illusions are enhanced with telepathy, allowing her to tailor her illusions based on her opponent's fears. Both sisters joined Pryor's first Sisterhood for different reasons as they don't get along.
9 Typhoid Mary
While Typhoid Mary is more commonly associated with Daredevil, she joined with the second version of the Sisterhood with the promise that Arkea would be able to fix her fractured psyche of dangerous multiple personalities.
Mary had a number of psionic abilities at her disposal that included telekinesis, telepathic hypnosis, and pyrokinesis, depending on which personality was dominant. Typhoid's time with the Sisterhood was beneficial as her personalities were reintegrated, though the team was defeated and disbanded shortly afterward.
8 Chimera
Not much is known about the dangerous mutant known as Chimera except that she comes from another dimension and is quite crazy, as her reasoning behind joining Pryor's Sisterhood was that she was bored.
Chimera is not only able to access other dimensions for weapons when needed, but she also was able to manifest powerful ghost-like energy dragons that she controlled but could also operate independently when needed, making her an incredibly dangerous member of the Sisterhood.
7 Lady Deathstrike
While Lady Deathstrike isn't a mutant, she transformed herself into a cyborg weapon in her mission of revenge against the enemies of her father, who had created the adamantium-bonding process that enhanced heroes like Wolverine.
She was rebuilt a few times by Spiral, who had some control over her after frequent rebuilds that led them both to join Pryor's Sisterhood. Lady Deathstrike is a skilled martial artist with cybernetic enhancements and adamantium-laced extendable claws along with a healing factor that makes her nearly unkillable.
6 Revanche
The woman known as Kwannon had her body stolen by Spiral and the Hand and used to house the mind of Betsy Braddock/Psylocke, which left Kwannon in Betsy's body with a fraction of her abilities that she used as the assassin known as Revanche.
While Revance eventually died, Kwannon lived on as a vengeful spirit who was promised her resurrection by Pryor for her membership in the Sisterhood. Kwannon later returned to life without Pryor's help, though she was freed from her vengeance and able to return to the X-Men.
5 Spiral
Richochet Rita was a stunt performer before she met Longshot, which led to her abduction by Mojo and torture and transformation by his scientist Arize into the six-armed "time dancer of death" known as Spiral.
Spiral would also transform other characters like Psylocke and Lady Deathstrike in her cybernetic "Body Shoppe," and she joined both versions of the Sisterhood for her own warped reasons. Spiral is a powerful sorceress and dimensional teleporter with enhanced cybernetics who has beaten the X-Men on her own numerous times.
4 Enchantress
Amora/Enchantress is an Asgardian who joined the Sisterhood after they were able to free her and restore her powers, which she then used to bring members like Selene and Madelyne Pryor back to life.
Enchantress is one of the most powerful sorceresses in Asgard, and she can use her abilities in a number of powerful ways, though she tends to focus on manipulating and influencing weak-willed men to do her bidding, even though she is more than powerful enough.
3 Arkea
Arkea and her brother Sublime were sentient bacteria and some of the first forms of life on the planet, though they fought over who would guide the development of Earth, and Arkea was exiled from the planet where she traveled and evolved across the galaxy.
When Arkea returned to Earth for revenge on her brother, she used her ability to take over any being, both organing and technological, to infect cybernetic characters like Omega Sentinel and advanced technologies to become Arkea Prime, though her body was destroyed by the X-Men who had formed to stop her.
2 Selene
The former Black Queen of the Hellfire Club is also an External known as Selene, whose life-absorption abilities have sustained her for generations as a dark mutant vampire sorceress with various psionic abilities and magical talents.
Selene exists in a constant cycle of death and rebirth that had apparently ended after she perished during a failed ritual in Necrosha, and she was resurrected by Enchantress and Arkea to add some much-needed power to the Sisterhood to help in the coming battle with the X-Men.
1 Madelyne Pryor
The evil clone of Jean Grey shares similar abilities to her genetic donor, though she also was altered by her exposure to a sliver of the Phoenix Force and her later dealings with demonic forces as the Goblin Queen before her death.
Pryor's telepathic ghost survived her death and sought out a new host body that could contain her powerful energies, which led her to create the first Sisterhood as she attempted to return in Jean Grey's deceased body. Arkea was later able to bring Madelyne back fully, and after Arkea was destroyed Madelyne was in control of the Sisterhood once again.