Void in the Force

This was a rare and unheard of phenomenom, where something or someone was completely dead in The Force. The only two beings who registered as non-existant in the Force were the Umbaran sibling, assassins Nyss and Syll Nenn. Both siblings could create a dark void in the force, making them undetectable to Force sense, and could make the Force inaccessible to others (though Jaden Korr and his clones were somewhat resistant to this), to the point that they nullified the force energy in lightsaber crystals causing them to shut off. After the death of Syll, Nyss Nenn felt that his ability had increased, when while his sister was alive, he had always pyschologically thought that she was an amplifier. It is unknown why these two beings were completely Void in the Force.

Granta Omega was also considered to be a void in the Force by Obi-Wan Kenobi, though he speculated that Omega might be using a strong self-concealment technique.

Behind the Scenes
It is important to note, that this power is not Force suppression, as to supress the force, the user needs to be able to access the Force in the process; the Nenn's had no force-sensitivity to begin with. It should also be noted that while the Yuuzhan Vong were invisible in the Force,they were not non-existent, evantually being sensed by some Jedi and were previously connected to the Force, until stripped of it, centuries ago by Yuuzhan'tar.This is basically a naturally occuring abomination similar to the destruction of Nathema, only the Nenn's were born this way.

Appearances

 * Riptide (novel)