A timeshadow was a version of a person that lived in an alternate timeline.
Each timeshadow existed simultaneously with a person in the galaxy and was an exact copy of that person. Though, when the person died, their body would vanish and be replaced by the timeshadow, allowing the person to cheat death. However, this only worked once and if someone was killed a second time, then they would remain dead.
When the Cularin system disappeared from the galaxy for ten years due to the temporal effects of the Darkstaff, the shifts in the timestream of the planet Cularin caused some of its residents to develop timeshadows of themselves. When the criminal Gust Toruna was gunned down down by a thug working for the crime lord Riboga, Toruna was replaced by a timeshadow of himself.