It is part of the Soulpower:
ability to detach his soul from his body, granting him super speed, by means of his soul quickly moving to a different place and his body following it almost in an instant. This acts to give him speed in short bursts (or long term use for long distance travel), and allows him to go anywhere his soul can get to, regardless of whether his body (under normal conditions) could or not (e.g., on top a statue to the right of his throne). He's able to fly with this ability.
He also has the ability to grab a person's soul out of their body, killing them, but he's unable to absorb the souls to become more powerful, but since the Soulpower recharges, he doesn't need to. This so called Soulpower he gained during his trip to the Underverse also grants him healing powers, which he can use to regenerate and to protect himself against harm.
Not sure of the script but the above comes from the only sites that spend anytime on it:
The Lord Marshal of the Necromongers in The Chronicles of Riddick was transformed into a "Holy Half-Dead" because he visited and returned from the Underverse, the Necromongers' promised land. He shows particular mastery of souls, as he can move his own soul separate from his physical body, giving the illusion of Super-Speed. He can also directly take hold of anyone else's soul, with the victim dying as soon as he releases it.
Checked the script, Soulpower is not explicitly named, just lots of references to his 'soul':
Now Lord Marshal spots the "officer" the one he saw rear of the hall -- and his soul flinches.
And he knew. His half-dead soul sensed I was behind him.
Closing on Lord Marshal. Just when we think
we've caught him unaware, a "soul" head turns inside his
physical head. His astral face stares at us for a moment
before the physical face catches up.
Lord Marshal approaches. Chillingly, a third arm -- red and
ethereal -- separates from his body. This "astral" arm
reaches inside the politico… fishes about for a moment…
then violently rips something out and throws it on the floor
for the everyone -- especially the gape-mouthed politico -- to see.
It's a human soul. Red and ethereal. Silently screaming at
the shock of being C-sectioned from the body of Politico #1.
An empty husk, he falls and dies.
He might have been able to use the Soulpower to see Vaako sneaking up on him, but it didn't save him from the unexpected Furyan he didn't anticipate bringing him down.