"This ship… is it his weakness? It should not exist, yet it cruises the darkness between the stars. He tore it from the mass shadows of Malachor, along with his fleet… that is a measure of his power."
Mandalore: [The Ravager] is barely holding itself together. The structural damage should have destroyed it long ago.
"The last Jedi conclave was on Katarr, a Miraluka colony. And all of Katarr was destroyed, all of the Jedi killed...Including Master Zhar...
As we see, Nihilus easily tosses around a Jedi Master and his former tutor but that is not all.
What Traya later says happened to her:
"And there would be those, like me, who have had the Force stripped from them." http://www.youtube.com/watch?v=D2bcS4uZWtY
"The Master suffers... If he can not feed, then the hunger begins to consume him The planet Telos... He may feed on something upon its surface to sustain himself a while longer."
"[Kreia] spoke of the Jedi academy here on Telos...and my Master was forced to come here." -Tobin
"If there are no Jedi here, then my Lord cannot feed his hunger. He will destroy the planet, the station... he will cleanse it of life. ...and if there are no Jedi below, he will have no other choice."
So, the Exile, Visas and the Mandalore all proceed to the bridge of The Ravager and confront Nihilus in this condition.
The subtitles aren’t in English but it’s the clearest vid I could find of this.
At 00:34, Nihilus stuns the Exile. The Exile and everyone else is at his mercy with no more than a gesture after turning around.
But he chooses not to. He chooses, because he “suffers”, to try and drain the Exile. (1:08) He then falls down before getting back up, withdrawing his saber and preparing to fight.
Jump to the end of the fight. After the Mandalore, Visas and the Exile have been assaulting him.
What were the results of that initial conflict?
Visas: “He... is too powerful...” (1:56)
So, the only canon account we have of how that first skirmish went was that apparently he was either beating the crap out of all of them or whatever they did had no effect. And this is him doubly weakened.
But yes, Nihilus does eventually lose the fight. If he had chosen to, however, he could have beaten the Exile in the first seconds of the fight. And the Exile overcame Nihilus with 2 assistants.
Kreia: it is a means of severing connections between life, the Force, and feeding upon the death it causes
(presumably what he did to Katarr)
Kreia on Nihilus:
"One cannot have power of that magnitude and still think and perceive the universe as we do."
"his mere presence kills all around him, slowly, feeding him."
Visas: I do not believe he knows his ship has been boarded. And if he did, he would not care. The extent of his power can not be put into words. And his perceptions have grown as well. To him...
Tobin: You are dust motes in a storm. A grain upon the beach and as insignificant as a body that orbits the graveyard of Malachor.
Canderous: If he’s so powerful, why hasn’t he stopped us, then?
Tobin: It is because he sees planets, stars...not people. To him, the planet below, the station with its teeming life, only that is massive enough to demand his attention.
Visas: He is a wound in the Force, more presence than flesh, and in his wake life dies… sacrificing itself to his hunger."
"You have taken this trophy from the remains of Darth Nihilus - it is the last surviving piece of the beast who died and was reborn in the shattered world of Malachor V.
Evil Never Dies: The Sith Lords says Nihilus is a Dark Lord of the Sith.
"Many times the title of "the last Dark Lord" has been erroneously applied. First the Dark Lord Naga Sadow, vanquished by the Galactic Republic in the Great Hyperspace War 5,000 years before the Battle of Yavin, was thought to be the last. Then a thousand years later, the fallen Jedi Exar Kun was considered the last of these dark siders' twisted kind. Then Darth Nihilus . . . then Lord Kaan . . . then Darth Vader."