Lucius the eternal has the ability to transform his killer in him again.
Since that day, Lucius has borne a peculiar blessing from his patron, Slaanesh. Whoever takes his chosen champion's life, and finds even a moment of satisfaction from the act, will find themselves undergoing a painful and gradual metamorphosis. When the transformation is almost complete, Lucius emerges from their discarded shell like a butterfly from a chrysalis. All that remains of his killer will be a screaming face trapped forever in the fleshy panels of his twisted battle plate.
Are there limits to this ability? E.g., as this blessing is linked to the Warp, could he transform a Pariah or would a Pariah be immune to this?
As Daft pointed out:
A Blank is the direct antithesis of Chaos as he or she possesses no presence within the Warp. Blanks are completely immune to daemonic possession and spiritual corruption by Chaos.
However, in the Horus Heresy Book "Nemesis", there is Spear, a Pariah which is bonded with a daemon:
He forced Spear to undergo a painful and vile Chaotic ritual, in which a minor daemon from the Immaterium was bonded with the former assassin.