This is my respect thread for the Nightsisters' leader Gethzerion. There was another respect thread for her, but given that it's incomplete, and its creator has left the site, I decided to make a new one with additional information on her powers.

Respect Gethzerion:

I'd also recommend reading this thread in blog format.

Power

Gethzerion is noted by Augwynne to be very powerful:

Augwynne looked at the distant clouds, unconcerned, and a brilliant branch of orange lightning with many tongues arced up into the sky, as if expressly for her to see. "Oh, she's very powerful, and very angry. But for tonight, she will not come."

-- The Courtship Of Princess Leia

Augwynne claims that Gethzerion is too powerful to be allowed to leave Dathomir:

Chewie roared and Augwynne said, “We can’t give Gethzerion a ship. She is too powerful. You can’t give her access to the stars.”

-- The Courtship Of Princess Leia

Luke Skywalker views Gethzerion as powerful:

He saw the ground coming up fast, two black-robed Nightsisters standing on the rocks. Luke dropped beside one of them. He shouted in warning. A Nightsister turned, readying a spell. Luke fired. She stood as if angered, flames smoldering from her cloak, and he realized that the Force must be strong in this one. The other ran off into the haze.

The lone witch glared at Luke. Gethzerion pulled back her hood to show the purpled veins in her face.

-- The Courtship Of Princess Leia

She's powerful enough to cause Luke to feel a tremor in the Force when she used her powers to try to find him:

They walked a hundred yards through the shallows, lay down on the beach. Luke could feel a tremor in the Force, like a thin probing finger of thought, Gethzerion stretching out with her mind, trying to find them.

-- The Courtship Of Princess Leia

Being their leader, she is the most powerful of the Nightsisters:

The most powerful of the Nightsisters was an aged crone named Gethzerion.

-- The Dark Side Sourcebook

Even in her younger days, she was far more powerful than her sisters:

Of the three sisters, Gethzerion was by far the most powerful of the siblings; she could even cast some spells silently-something only their mother and Clan Protector Tannith could do.

-- Cracken's Threat Dossier

Gethzerion grew in power during her exile from the Singing Mountain Clan:

As Gethzerion grew in fame and power, so did the defections to the Nightsisters Clan.

-- Cracken's Threat Dossier

Gethzerion and the other Nightsisters grew quickly in power:

The Nightsisters were convinced that the other Witch clans were below them, weak and insubstantial. They found their power grew quickly, and while their flesh wilted into haggard, bruised and wrinkled husks, the shadowy energy they could bring forth gave them a twisted sense of joy no other Witch on Dathomir could possibly know.

-- Cracken's Threat Dossier

Gethzerion was repeatedly stated to be a threat to Emperor Palpatine, the most powerful Sith lord in history, with the latter being disturbed and even "stunned" by the depth of her power, stranding her on Dathomir as a result:

When he was alive, Emperor Palpatine had known of Gethzerion. He allowed her twisted usage of the dark side of the Force as long as she was trapped on Dathomir, where an Imperial penal colony housed political prisoners.

Knowing the extent of her powers, though, he decided it would be dangerous to let her get off planet, so Palpatine ordered the orbiting airfield destroyed, in the process stranding many of his own people.

-- The Essential Guide To Characters

With the rise of the New Order, Imperial forces constructed orbital shipyards and a penal colony on Dathomir's surface.

But after Emperor Palpatine learned the power of the Nightsister's leader, Gethzerion, he ordered all prison's ships destroyed to prevent her from leaving the planet.

-- The Complete Star Wars Encyclopedia

But the Emperor, who sensed Gethzerion's power through the Force, realized that once Gethzerion mastered the controls of a shuttle, she could reach the orbiting docking facility, and from there spread her influence to the rest of the galaxy, one day perhaps even challenging him. The Emperor ordered the orbital docks destroyed, abandoning the lmperial forces of the penal colony to Gethzerion and the Nightsisters.

Ships were assigned to periodically the planet and make orbital scans to ensure that the Nightsisters were still confined to Dathomir, but were given strict orders never to land.

This state of affairs continued for many years, until the death of the Emperor.

-- The Dark Side Sourcebook

When the Nightsisters made contact, the Emperor was stunned by the depth of their leader Gethzerion's power. Wanting to keep her abilities safely bottled up, Palpatine ordered the prison's ships destroyed from orbit; the stranded guards were enslaved by Gethzerion and her twisted followers.

-- The Essential Guide To Planets And Moons

Chewie roared and Augwynne said, “We can’t give Gethzerion a ship. She is too powerful. You can’t give her access to the stars.”

“Han,” Leia said, “Augwynne has filled me in on a few things. I believe the Emperor himself was afraid of the Nightsisters. That’s why he interdicted this planet. Years ago, he started a nice little penal colony here, not knowing about the Nightsisters. When he learned about them, he blew the planet’s airfield from orbit and stranded hundreds of his own people here, along with the prisoners, rather than risk letting Gethzerion escape. That’s how frightened he was of Gethzerion".

-- The Courtship Of Princess Leia

It should be noted that other sources state or suggest either that Palpatine was afraid of the Nightsisters as a whole, or that he was disturbed by Gethzerion's growing strength, rather than her actualized power, with two of these statements being from more recent sources. And while there are more sources portraying Gethzerion herself as a threat to Sidious, there are almost as many of them stating otherwise, and since two of them are more recent, the value of her previous accolades is questionable:

A recently established prison colony on Dathomir brings the Nightsisters to the attention of Emperor Palpatine, who gauges the possibility of them being a threat to his reign.

-- Jedi Academy training Manual

The newcomers to Dathomir promptly encounter the Witches of the planet. The warriors of the Singing Mountain Clan are noble and fearless females who enslave males as breeding stock and ride atop trained rancor beasts. The Witch named Teneniel Djo at first wants to enslave Luke and Isolder, but she later comes to respect them. Such is not the case with the wicked Nightsister clan ruled by Gethzerion. They are cruel and evil magic wielders who long to escape the blockaded world. Years earlier, Palpatine was alarmed by their growing power and purposely stranded them on Dathomir.

-- The Essential Reader's Companion

Eight years earlier, the Emperor had constructed a prison on Dathomir, but when he'd learned of the Nightsisters, he had destroyed all of the prison's starships from orbit-better to lose a prison than to let rival Force users loose upon the galaxy.

-- The New Essential Chronology

Her powers grew through devotion to the dark side, and she was determined that her clan would rule, and eventually, escape the planet on which she had been stranded by Emperor Palpatine, who had been disturbed by Gethzerion's growing power.

-- The Complete Star Wars Encyclopedia

Force knowledge

Gethzerion studied part of The Book of Law, gaining access to some of the forbidden magic of the Witches of Dathomir:

Gethzerion and Baritha began seeking out other exiled Force witches to join their new clan, which they called the Nightsisters. The Nightsisters explored the forbidden magic that Gethzerion could recall from The Book of Law, and through trial and error learned to master the dark arts of Dathomir.

They fought periodic battles with the other clans of Dathomir, and whenever possible, they promised to spare captives if they would forswear their old clan and join the Nightsisters.

-- The Dark Side Sourcebook

Gethzerion wrote the Book of Shadows, which contains detailed information about the Nightsisters' magic spell she created, as well as about the dark side in general:

When Gethzerion created the Nightsisters Clan, she decided that they needed their own book of lore to pass down through the generations-if only to tell the story of how thei clan was formed. The Book of Shadows goes into quite a bit of detail about the dark side of the Force as well, providing the reader advice on using dark side powers.

-- The Dark Side Sourcebook

Gethzerion taught her pupils that the ancient text, the Book of Law, was created by Allya after she had become old and weak. That Allya's power had always been on her own ends, and that when she began to lose control of senses, she fell into a world of self-pity and despair. A place, according to Gethzerion, no self-respecting Witch would allow herself to stumble into.

Gethzerion began compiling her own tome of learning. She created spells for her Nightsisters, and would make them practice their chants and songs until they were hoarse. Only a very few of their kind were allowed to assist in the writing of the Book of Shadows, that tells of the Nightsisters future glories among the heavens. From the beginning Gethzerion knew that she would one day leave Dathomir, taking her army of Nightsisters with her.

-- Cracken's Threat Dossier

Alter Environment

Gethzerion can summon storms via Alter Environment;

She summons a Force storm around her dwellings, seemingly just by being angry, with Augwynne commenting that she is very powerful, and C-3PO wondering how much power output she can produce:

Outside, through the open portals, Han could see fierce storm clouds in the distance, flashing lightning. The stars here burned fiercely above the tree-covered mountains. Around him, the witches laughed and taught their daughters spells in the shadows. The young girls wore shirts and pants of simple hides, not the elaborate costumes of the fully trained witches. Yet the witches seemed more casual, more cozy around their children. They removed their headdresses and let their hair down. Without their full attire, they weren't so intimidating, and reminded Han only of rugged peasants. The witches' husbands worked silently, dressed in tunics of woven plant fibers, serving meals to the women so quietly that Han almost felt as if they must be communicating telepathically.

Augwynne sat nearby so that she could speak softly to Han and Leia. She noticed how Han frequently eyed the distant storm. "Do not worry yourself," she said. "That is only Gethzerion, thrashing in impotent fury. But she is too far away. There will be no Force storm tonight."

"Gethzerion is making that lightning?" Threepio asked, his eyes suddenly bright. "Why, I wonder how much power output she can produce."

Augwynne looked at the distant clouds, unconcerned, and a brilliant branch of orange lightning with many tongues arced up into the sky, as if expressly for her to see. "Oh, she's very powerful, and very angry. But for tonight, she will not come."

-- The Courtship Of Princess Leia

She manipulates clouds and smoke to take the form of her face:

“This is no weather for anyone,” Luke said, sniffing the air. The clouds were not the gray of storm clouds filled with heavy rain or the white of billowing clouds that promise summer sprinkles. These were dense clouds of dirt and soot rather than of water. He looked up, and suddenly the clouds above the valley swirled, as if a hand had waved above a cooking fire. Gethzerion’s face filled the sky, a face made of reddened smoke that frowned down upon them, eyes twitching. Then the face dissolved, but Luke was left with the uncanny feeling that Gethzerion was still up there, hidden behind the clouds, watching them. The rancors snarled and backed away from the cliff.

-- The Courtship Of Princess Leia

Gethzerion and other Nightsisters manipulate smoke and charge the air with static electricity:

The brown smoke hung ominously above like a pall to cover the world, yet it was utterly motionless. Somehow, the Nightsisters were manipulating the smoke, using the Force to wield it like a hammer. The air felt charged with static electricity.

-- The Courtship Of Princess Leia

Gethzerion summons storms to batter Luke and Tenel Djo:

The main obstacles to Gethzerion's plan were the younger Tenel Djo of the Singing Mountain Clan, and a Jedi named Luke Skywalker. Force storms Gethzerion conjured up and Zsinj's orbital nightcloak- which was causing Dathomir's atmosphere to cool-battered the Jedi and Nightsister of the light side, but they still held their own.

-- The Essential Guide To Characters

Telepathy/Force Sense

Gethzerion can instill fear in the minds of other people via Force Fear:

She can conjure illusions:

She stretches out with her mind to find Luke and his companions:

They walked a hundred yards through the shallows, lay down on the beach. Luke could feel a tremor in the Force, like a thin probing finger of thought, Gethzerion stretching out with her mind, trying to find them.

-- The Courtship Of Princess Leia

While far away from her, she gives Baritha instructions:

Baritha shouted, "Gethzerion, we have found the offworlder. He has a starship, but the clan sisters will not give him to us!" Han could hear a humming in his ears, almost as if a fly buzzed within his skull. The hair raised on his neck, and he knew for a certainty that no matter how far away this Gethzerion was, she had heard Baritha's call and was now giving the woman instructions.

--The Courtship Of Princess Leia

Gethzerion summons the Nightsisters for war, and telepathically hunts Barukka:

“Please,” Teneniel said, “we’ve come for your help!”

Barukka stayed outside the light of the fire, watching them like some wild animal. Her face was badly bruised. “You are in danger,” Barukka said at last. “Gethzerion has been summoning the Nightsisters for a war. I can feel her summons, pulling at me. You are her enemies.” Barukka’s voice was strangely contemplative, as if she were studying her own feelings.

“But we are not your enemies,” Luke said.

“Mother Augwynne told me that you petitioned to join the Singing Mountain clan,” Teneniel said. “We would like to welcome you back fully as a sister some day.”

“Yes,” Barukka said distantly. “She has chosen to leave the Nightsister clan.” She said it as if she were speaking of someone else, someone who was not in the cave, and Leia knew that this woman was not sane.

“You chose to leave the Nightsisters,” Teneniel said.

“Yes,” Barukka whispered, as if remembering.

“Will you help us?” Teneniel asked. “We need to go to the prison, to find some parts for a ship. Can you tell us where to look?”

Barukka stood unmoving for a long moment, frowning in concentration. She began to tremble, and whispered, “No, I can’t.”

“Why can’t you?” Luke said. “Gethzerion has no power over you.”

“She does!” Barukka said. “Can’t you hear her calling me? She hunts me! Even now, she is stalking me!”

“Does she call to you?” Luke asked. “Do you hear her voice in your head?”

“Yes,” Barukka said.

“What does she say?”

“She rails against me, curses me,” Barukka answered. “Sometimes I hear her at night, as if she is standing by my bed.”

“You two must have been close,” Luke said.

Teneniel said, “Gethzerion is her sister.”

-- The Courtship Of Princess Leia

She tries to probe the minds of Luke, Teneniel, Isolder and Leia:

The Nightsister nodded thoughtfully. Luke could feel her trying to probe them, and he almost pulled his blaster. Instead, he channeled the Force, let it flow into the witch, quiet her suspicions.

--The Courtship Of Princess Leia

While far away from him, she telepathically communicates with Han Solo, showing him an event that was taking place in that moment:

Suddenly, something shoved its way into his consciousness, as if an invisible hand had pushed through his skull. It was an odd sensation that left him feeling violated, dizzy. Very clearly, an image formed in Han's mind, a vision of dozens of men and women in orange coveralls, standing in a well-lighted room. They were looking up curiously, gazing around at walkways above them. On the walkways stood stormtroopers with blaster rifles. Han recognized the prison.

General Solo, Gethzerion's voice crawled through his mind. I hope you will find this amusing. As you see, I am here at the prison with dozens of your kind below me. I trust that you are a compassionate man, a caring man. I suspect you are. As you know, I have struggled through various means to cause you to come to me. Perhaps this will convince you.

A hand waved in front of his face, a hand partly concealed by a black robe, and Han perceived that he was viewing the scene through Gethzerion's eyes. The stormtroopers looked at her waving hand, began firing into the crowd. Men and women screamed and scattered, trying to run from blaster fire, but the gates back to the cell blocks had closed, and they could not escape. Han threw his arm in front of his eyes, tried to blind himself to the atrocities, but the vision persisted. He could not close his eyes against it, for the vision remained even when his eyes shut. Nor could he turn away, for the images followed him: a woman ran shrieking below the parapet, and Han saw Gethzerion's hand go up, blaster aimed as if he were staring through the laser sights, and she snapped a shot into the woman's back. Gethzerion's victim spun with the impact of the blast, then collapsed, stunned, as Gethzerion pulled off another shot. A man beside the dying woman raised his clasped hands, pleading for Gethzerion to spare them. The witch fired high into his right leg and the prisoner was thrown to the floor to die slowly as he bled to death.

These fifty people are already dead, Gethzerion said, forcing Han to continue viewing the murders. They die because of your stubbornness. When my stormtroopers finish with them, I will round up five hundred more just like them, bring them to this room to die. But you can save them, General Solo. I will send a Nightsister to pick you up at the foot of the fortress in my personal hover car. If you are not there to meet her in one hour, then those five hundred people will die, and you will get the privilege of watching. If you do not surrender after that, you will watch the deaths of another five hundred, and another. As I said, I trust that you are a compassionate man.

-- The Courtship Of Princess Leia

Force Heal

Gethzerion can heal herself:

Nightsisters magic/Shadow Magic

Gethzerion knew many of the Shadow Magic spells listed in Cracken's Threat Dossier, and it is believed she had access to many more:

She honed her magical skills during the years of her exile:

During her time in exile, Gethzerion spent her years honing her shadowy craft.

-- Cracken's Threat Dossier

She created a number of spells, teaching them to the other Nightsisters:

She created spells for her Nightsisters, and would make them practice their chants and songs until they were hoarse.

-- Cracken's Threat Dossier

She seemingly uses a spell to mortally wound Luke Skywalker, ripping blood vessels in the latter's brain and leaving him to die, though the latter was seemingly caught off guard:

“I’ve met your kind before,” Luke said. “Listen to me, Gethzerion: turn away from the dark side before it is too late!”

Gethzerion nodded thoughtfully. “Pardon me if I say that I don’t find you to be very impressive, young Jedi. It’s a shame that you must die before you have a chance to witness how I make your friends writhe.”

She pointed a finger at Luke, and before Luke even recognized her evil intent, a ripple of Force slammed into him. White lights exploded behind his eyes, and the right side of his face felt as if it had been smashed by a hammer. His left arm and right leg crumpled under their unbearable weight, and he dropped to the ground on one knee, stunned. All the noise and blaster fire and screams of pain died away, became a distant roaring. Gethzerion pointed at him again, twitched her finger, and his eyes lost focus. He felt the hammer blow to his left temple, dropped to his side and rolled over to his back, gasping. Luke stared up at the sky, watching streams of rocks hurtling above him—some propelled by the Force, others hurled by rancors.

Time seemed to slow. His head throbbed, pounding to the same rhythm as the beating of his heart. His face had gone cold, numb, and Luke realized distantly that Gethzerion’s spell had ripped open blood vessels in his brain, and he was about to die, one among hundreds of fatalities on this battlefield.

So this is how it would have been, if Vader had tried to kill me. Who had Luke been kidding? Teneniel had been right, Luke was no warrior. Ben, Luke thought. I failed you. I’ve failed you all. And suddenly there was a wave of pain, and Luke tried to remember who he’d just been talking to, tried to think of a name, someone he could call for help, but his mind was numb, empty, like the vast deserts of Tatooine lying naked beneath setting suns.

-- The Courtship Of Princess Leia

Long before her prime, Gethzerion was capable of casting some of the Witches of Dathomir's spells silently, which only Augwynne and Tannith could do. Later, she could use the magic of the Nightsisters without the need for chanting or rituals, intimidating and forcing her will on others with it:

The Nightsisters were Force wielders whose genes had been developed via selective breeding to assure power. The majority of them believed they had to chant, sing, or perform rituals and spells to use their magic.

Only Gethzerion realized they could use their Force talents without rituals; she used her "powerful" solo magic to intimidate and force her will on others.

-- The Essential Guide To Characters

She discovered that she was able to cast spells without the aid of chanting and other more primitive rituals.

-- Cracken's Threat Dossier

Of the three sisters, Gethzerion was by far the most powerful of the siblings; she could even cast some spells silently-something only their mother and Clan Protector Tannith could do.

-- Cracken's Threat Dossier

Along with other Nightsisters, she used her magic to make the Imperials on Dathomir her slaves:

Gethzerion and her clan of Nightsisters quickly took over the Imperial prison that held the Empire's rogue scientists and designers. Using their Shadow Magic, the Nightsisters made the Imperials their slaves. Those that resisted were promptly disposed of.

-- Cracken's Threat Dossier

The Imperials fought back and won, beginning a years-long campaign against the Force witches of Dathomir. Even so, Gethzerion, the leader, periodically visits the Imperial base and controls the minds of its troops and even its commanding officer, trying to gain access to a starship, so that she can spread her evil among the stars.

-- Insider 65

Force Lightning

Gethzerion knows Force Lightning:

Telekinesis

Long before her prime, she causes a boulder to fall from a mountain, crushing Kara'Teel's body in the process:

Augwynne had left the protection of their mountain fortress, taking to the fields to watch her husband catch a giant wuffa worm. One telekinetic tug from Gethzerion's mind, and the loose rock high above would come crashing down upon the Clan Mother's head. Augwynne would be caught completely unaware. But all did not proceed according to plan.

When the boulder began to fall from the mountain heights, it was her sister Kara'Teel, not Augwynne, who paid the price. Sacrificing her life so that her mother might live, Kara'Teel pushed Augwynne out of the boulder's path-her body crushed in the process.

-- Cracken's Threat Dossier

Gethzerion telekinetically tortures Han Solo by crushing a number of his bones:

Gethzerion twitched her finger, and Han jerked upright, found himself with his feet dangling in the air, held by an invisible cord around his throat. Gethzerion watched him intently, began to sing, swaying from side to side. He felt the noose around his neck tightening. Han chocked, kicked, fought to break free.

"I wonder what your thermal detonator would have done to me," Gethzerion reflected, still swaying. "I suspect it would have blasted my flesh into scraps, and broken my bones, and fried me all at once. So I think I shall do all of these things to you—but not so hastily. Not all at once. I think we shall work from the inside out. First I'll snap your bones, one by one. Do you know how many bones there are in the human body, General Solo? If you do, just triple the number, and you'll know how many bones you'll have when I finish with you. We'll begin with your leg," Gethzerion said. "Listen carefully!" She twitched her finger, and the tibia in his right leg made crackling sounds. A painful spasm made its way up to his hip.

"Aaaghh," he cried—and saw something over the desert. There about two kilometers off he saw the running lights of the Millennium Falcon speeding toward them, only meters above the ground.

Gethzerion smiled in satisfaction. "There now, you have three bones where you had but one."

Han tried to stall her, tried to think of anything that would slow her for a moment. "Listen," he strained to speak. "You aren't going to do this to, to, to my teeth, are you?" he said, unable to think of anything else. "I mean, uh, anything but the teeth!" He glanced around the compound. Several Nightsisters were coming out the bottom of the towers.

"Oh, yes, the teeth," Gethzerion said, and she twitched her forefinger. Han's right upper rear molar exploded with a popping sound, and the stabbing pain shot through his ear and upper face, until it felt as if Gethzerion had grabbed his eye at the socket and were intent on pulling it through the roof of his mouth. Han silently cursed himself for giving her nifty ideas. The Falcon wasn't getting here fast enough, and Han shook his head.

"Wait!" he cried. "Let's talk about this!" and Gethzerion wiggled her forefinger again. The upper left rear molar snapped, and suddenly there was a whooshing sound as the Falcon fired its missiles.

-- The Courtship Of Princess Leia

She kills Melvar and 100 stormtroopers, seemingly with casual ease:

Melvar got up, tried to recover his dignity, and took the detonator. "Thank you," he grunted.

"Ah, and allow me to do you one more favor!" Gethzerion whispered, stepping forward. "By giving you this—” Her eyes opened wide, blazing, and she made a raking motion with her index finger. Beside Han the general gasped, reached up to hold his temple, then staggered forward a pace. "A simple death!" Gethzerion cackled. All around Han, a hundred stormtroopers crumpled simultaneously, some of them staggering a step or two, some firing blaster rifles in the air so that Han instinctively ducked. Within three seconds the stormtroopers lay on the ground like drugged birds, unmoving. Han looked up at the carrier, waiting for the ship to open fire. Nothing happened. The ship remained deathly still.

--The Courtship Of Princess Leia

Physical Capabilities

Speed/Agility

She avoids a blaster shot by crouching:

A volley of blaster fire shot from the dorsal turrets with pinpoint accuracy. Gethzerion crouched as the bolt ripped through the air where her head had been.

-- The Courtship Of Princess Leia

She avoids blaster fire by leaping:

She leaped away from the ship, jumped and twisted just as another volley tore beneath her.

Han got a spooky feeling about this. Nobody could fire a ship’s blasters with such accuracy. He rolled under the gangplank to take cover from flying debris. The heavily armored guard droids on all six prison towers spun on their turrets and opened fire on the Falcon, blasting with their cannons.

-- The Courtship Of Princess Leia

Gethzerion jumps faster than Han Solo would have believed possible:

Gethzerion must have recognized that staying on the ground to fight was futile, for she leaped up the gangplank of the Imperial ship faster than Han would have believed possible. The carrier’s turbines whirred to life before the gangplank even raised, and the air around the ship took on a blue sheen as shields activated. This was an Imperial personnel carrier—fully armed and shielded, nothing for the Falcon to toy with.

-- The Courtship Of Princess Leia

Click here to see my list of respect threads