Darth Vectivus is an extremely obscure but nonetheless unique and fascinating Sith Lord, because supposedly he was not corrupted by greed and other negative traits that beset almost every other Sith - instead, he was a regular businessman who merely used his dark side power to expand his knowledge of the Sith and the dark side.

Respect Darth Vectivus:

Power

Each Banite Sith Lord grew more powerful than the last. Darth Vectivus' successful ascension to Sith mastery makes him more powerful than any of his predecessors and vastly more powerful than the likes of Darth Bane and Darth Zannah:

For a millennium, the Sith maintained the order in secrecy, passing down their evil heritage. As they gained knowledge of the dark side of the Force, their powers increased with each generation.

Source: Episode 1: The Phantom Menace Scrapbook

Ultimately, Bane's plan produced more powerful Sith Lords with every generation.

Source: Force & Destiny

For a thousand years we continued to follow Bane's Rule of Two, existing in the shadows, biding our time, growing in power, feeding our hatred.

Source: Insider #88: Heritage of the Sith

"Bane's power has been passed down for a thousand years. I vow to be its last recipient."

Source: Book of Sith: Secrets from the Dark Side

Force Ghost

Force Ghost is an esoteric technique allowing one to maintain their identity and consciousness in the afterlife in the form of a spirit, which allows them to influence the material world without being a physical entity.

Upon dying, Vectivus was able to use the Force to preserve his consciousness and identity as a Force Ghost after death (though Vectivus's Ghost was unique in that it was linked to another living being, indicating relations to his Force Phantom technique):

"Well done." That was a smooth male voice from behind her.

She spun, the move carrying her up a meter into the air.

Behind her stood a human man, dignified of bearing, his dark beard cut close in an elegant style. He was tall and a trifle overweight, but his loose-fitting black garments suggested that he was carrying around some muscle as well as fat. A silver lightsaber hilt, inlaid with polished black stones shaped like diamonds, hung from his belt.

Nelani drifted to the floor again and kept her own lit blade between them. "Who are you?"

He shrugged. "I doubt you’d know my birth name, but the other you may recognize. I am Darth Vectivus."

Nelani waved a hand at the caverns around them and gave him a smirk. "The Master of all this."

"Once, maybe. Now I’m merely a ghost. Or perhaps less."

"What would be less?"

"A remnant. A sliver of a ghost." He looked just a bit unsettled. "Even as I speak, I am unaware of myself. Of thinking, of decision making. Could I, in fact, be nothing?"

"No, I can feel you. Gleaming in the Force. Shining with the dark side."

He shook his head. "That’s not me. That’s whomever I am connected to."

"Connected to?"

Now it was his turn to wave around. "Every phantom you see here, every one you encounter, is connected to something that is distinctly real, distinctly alive-though possibly far, far away. Every time you struck a mynock, a living being somewhere suffered the pain and injury you inflicted."

Source: Legacy of the Force: Betrayal

As a Force Ghost, Vectivus was able to change his appearance at will, taking the form of Emperor Palpatine before reversing back to his natural appearance:

"Would it help if I took on a more hateful form? A piranha-beetle in human guise?" Vectivus’s clothes shimmered and flowed. Suddenly he was in a full-coverage cloak and hood, his face in deep shadow. He reached up with suddenly white, suddenly wrinkled hands to pull back the hood and reveal the pallid, almost reptilian features of Emperor Palpatine, Darth Sidious, dead now for more than thirty-five years.

His voice, too, was Palpatine’s, insidious and cloying. "How about this? Could you strike this down?"

"Not while you’re connected to an innocent life."

Palpatine rose and, shimmering as he did so, was Vectivus again by the time he was on his feet. His expression was sympathetic, but a bit pitying. "Jedi girl, you’re not strong enough to save lives. You’re not strong enough to sacrifice one to save many."

Source: Legacy of the Force: Betrayal

Vectivus's Ghost was able to disappear into the Force, and upon doing so, his Force Phantoms vanished with him:

Vectivus shrugged. "Perhaps I did. I wouldn’t know." Then he faded from sight, and as he disappeared, the susurrating noise of the mynocks wheeling overhead also vanished.

Nelani spared a look upward. They were gone, leaving not even a trace in the Force.

Source: Legacy of the Force: Betrayal

Force Phantom

Force Phantom is an extremely esoteric Force ability invented by Darth Vectivus himself. The technique allowed one to project phantasms across the breadth of space, linking them to a living being somewhere in the galaxy, and sustaining the manifestation of such phantasms with a nexus of dark side energy.

Darth Vectivus invented and mastered the Force Phantom technique, which he could teach others through his holocron. The Force Phantom technique was thought lost by the time of the Legacy era and was coveted by Lumiya, Alema Rar and the One Sith alike:

"It seems that among the resources she inherited from Lumiya is a Force technique permitting her the projection of phantoms across space. It appears in every way to match the lost technique of Darth Vectivus."

At those words, the murmur rose again. "Vectivus's history is clear. He was a fraud, someone muttered."

"A fraud with an art that would benefit us all," said someone else.

Source: Legacy of the Force: Fury

The white-eyed man considered. "Very well. You were correct, Dician. This is of highest priority. We will not concern ourselves with a cloaked ship, but assign a fully armed warship to the task. I am recalling the Poison Moon and assigning it to you for this mission. It will be equipped with explosives sufficient to destroy an asteroid. You will use it to locate the dark side energy source used to power Vectivus's Force phantom technique and obliterate it. You will obtain any Sith artifacts in Alema Rar's possession. You will also capture Alema Rar, or, if circumstances warrant, kill her."

Source: Legacy of the Force: Fury

Vectivus's Ghost was able to summon hundreds of Force Phantoms in the form of mynocks, with enough realism for Ben Skywalker to sense them in the Force. As Vectivus vanished, the mynocks did as well, indicating that he was responsible for their presence:

"We have company."

Ben looked down at her, then around, then up.

Above him, ten meters up, a pair of eyes stared down at him. They glowed blue in the reflected light of his lightsaber blade. They were not human eyes, but slitted and triangular.

Beyond them were more, hundreds of pairs of eyes, cool and unblinking. Ben shook his head. He’d had that portion of stone wall in sight as he’d approached the wall. There had been no creatures there at the time. He reached out for them within the Force, and could feel them there, hundreds of them, strong in dark side energy. "Not good," he said.

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Now Ben could hear rustling, hissing that sounded like muffled, sibilant speech, from above-from hundreds of sources above. "They’re going to swarm us," Nelani said. She sounded rattled. As if her words were a cue, a form of permission, the eyes above suddenly descended en masse, pouring downward as if carried by a waterfall. Nelani’s lightsaber snapped into life, adding a yellow-white glow to the proceedings. Ben raised his own blade in a high defensive stance.

The first wave of descending creatures broke before it reached the Jedi, splitting into two streams, each headed a different direction parallel to the stone face. But two of the creatures did not veer away. One came at Ben, one at Nelani.

Ben darted to one side-or tried; despite having some experience in low-gravity environments, he wasn’t accustomed enough to them for appropriate movements and tactics to be instinctive. He pushed off but floated mostly upward, straight toward his attacker.

No matter. The creature-revealed in the light of Ben’s lightsaber to be a fleshy stretched wing with eyes at one end, a tail at the other, and a wet mouth toward the center of its underside, something like a mynock-flew straight at him. Ben swung, felt his blade cut into skin and meat, and was propelled back down by the impact as the two halves of the beast hurtled lifelessly past him, one to either side.

The soles of his feet hit stone again. He absorbed as much of the impact as he could with his knees and did not bounce up very far this time.

The two mynock halves were partly embedded in the stone, and as he glanced at them, they slipped beneath the stone’s surface like two halves of a boat sinking. They left nothing behind-no blood, nothing.

"They’re not real," Ben said.

"Projections of the Force," Nelani answered from behind. "So they can’t really hurt us, right?"

"Wrong." Her tone chided him. "You know better than that. It’s like saying A laser beam can’t hurt me-it’s only light, right?"

"I was just hoping."

"Oof." Nelani sounded as though she’d taken a shot to the gut, and her lightsaber winked out instantly.

Heedless of the swarms of mynocks overhead, Ben spun, the motion bouncing him a couple of meters up.

Source: Legacy of the Force: Betrayal

Vectivus shrugged. "Perhaps I did. I wouldn’t know." Then he faded from sight, and as he disappeared, the susurrating noise of the mynocks wheeling overhead also vanished.

Nelani spared a look upward. They were gone, leaving not even a trace in the Force.

Source: Legacy of the Force: Betrayal

Vectivus explains the nature of Force Phantoms, and that they are all connected to something real. He explains that each Phantom that is struck, a living being somewhere in the galaxy suffered the pain and injury inflicted by that strike. He reveals that his own Force Ghost, in reality a Force Phantom, is also connected to somebody else in the galaxy:

Now it was his turn to wave around. "Every phantom you see here, every one you encounter, is connected to something that is distinctly real, distinctly alive-though possibly far, far away. Every time you struck a mynock, a living being somewhere suffered the pain and injury you inflicted."

With his statement, a knot of sickness formed in Nelani’s stomach. "You’re lying."

"No, I’m not. You struck, and somewhere, some creature, perhaps a baby bantha, squealed in pain and was severed, killed before the disbelieving eyes of its mother-"

"Stop it."

"Why? It’s the truth. Baby banthas are quite cute, you know. A terrible shame to see one cut in half."

"You’re sick."

"But perhaps it wasn’t cute little baby banthas. Perhaps it was piranha beetles. You wouldn’t mind cutting piranha-beetles in half, would you? Or perhaps Kowakian monkey-lizards." He shook his head. "They say that every creature is cute when it is a baby. A mechanism of nature to help creatures reach the age of reproduction. But it’s not true of every species. Have you seen immature monkey-lizards? Ugliest little larvae in the galaxy." He shuddered.

"What do I have to do to shut you up?"

"Oh, that’s simple. Kill me." He took a bounding, gliding step forward. "Sweep your lightsaber blade across my neck, topple my head from my shoulders. The mynocks will go away, and you’ll be able to find your way back to your friends." He landed only two meters from her and knelt before her. "Go ahead."

"You can’t be that anxious to die."

"I died centuries ago." Darth Vectivus bowed his head. "So I won’t feel anything. Go ahead and strike."

"And what about the life you say you’re connected to?"

Vectivus looked up again and grinned at her. "He or she will become a free-floating head, I’m afraid, rather to the surprise of everyone in the vicinity. ’Why, look, Father, Mother’s performing a new trick. Mummy? Mummy?"

Source: Legacy of the Force: Betrayal

Force-Flash

Force-Flash is a Force power with two uses. The first was the brief disabling of a droid or security camera (and related electronics), causing a brief period of static. Another usage enabled a Force user to generate a burst or flash of light for varying purposes, such as to blind another being.

Darth Vectivus' Force Ghost uses the Force to briefly illuminate the rails behind Nelani Dinn:

He gestured at Nelani - no, beyond her, and she felt a pulse of Force energy in the distance behind her.

She moved, a floating bounce that allowed her to turn but keep Vectivus in the periphery of her vision. In the distance, where Vectivus gestured, the rails that had borne Brisha’s car to these depths were briefly illuminated. Even when the light faded, she could still feel them, could mark their presence in the Force as though they were living things.

Source: Legacy of the Force: Betrayal