In 0 BBY, Sasori Vader, having somehow managed to take over a Jawa sandcrawler, imprisoned two Jawas (who had also managed to kidnap R2-D2 earlier) and incarcerate them in the bridge area of what used to be their sandcrawler. The young Luke Skywalker then made his way to the sandcrawler in order to free his droid friend and confront Sasori Vader, who had taken the shape of Darth Vader. During the ensuing fight, Sasori Vader turned back into its true form, but he was eventually defeated and killed by Skywalker.
Luke Skywalker confronts Sasori Vader in a Sandcrawler.
Sasori Vader was one of the stage bosses in the Japanese Star Wars 1987 video game. The game featured various fake Vaders which all happened to be shapeshifting monsters. The canonicity of this game and the creatures it features is dubious.
According to both "Game On!," an article published in Star Wars Insider 135, and the game manual, the fake Vaders (Clados, Gyaos, Sasori and Wampa) were "intended as illusions representing Luke's fears, like the Cave of Evil scene in Empire Strikes Back." However, since those game opponents were able to kidnap Luke Skywalker's allies and hold them prisoner, this article assumes they were real creatures rather than illusions. Additionally, the Vader-shaped figure that Skywalker fought in the Cave of Evil was more than mere illusion, being in fact a protean dark side entity known as the Dark Spirit.
In the game and the original Japanese language game manual, the character is called Sasori Beidā (サソリベイダー). While Beidā is a transliteration of "Vader" in Japanese, Sasori means "scorpion."