Duplicity

This species has no true form and poses a dead body making that their new host, and can mould the vessel to appear like any other race. This transformation is painful but otherwise indistinguishable from individual copied. To make it worse is they can mimic the sounds of the individual as well, but they are required to hear and see them in order to create the effect.  However, they don't know they possess the vessel of someone who has died and start gaining fragmented memories of the vessel's past life.
They are really rare after the Liren hunted them out of Koldkom. They prove vulnerable to fire causing their form to dissipate in contact with fire. They are in fact ghosts from the shells of an arctic tortoise race.