On Dantooine, a duplicate of Darth Vader came into being, only to be terminated by the genuine Darth Vader.
Sometime before the events of 0 ABY, Darth Vader made his way to ancient Jedi ruins situated on Dantooine, which happened to contain a functional, yet unattended, cloning installation. He was surprised by automated security turrets, resulting in the deaths of his entire team. During this encounter, Vader sustained injuries, and some of his blood remained at the facility.
The experimental cloning automatons in charge of the facility, operating under the belief that they were following their directives, utilized this blood sample to generate a Vader clone. The droids then employed a peculiar technique (applied to all clones produced there), imbuing the clone with Vader's personality, derived from mental echoes left by the original subject. However, as with the other clones created at the facility, this process was flawed, resulting in the clone possessing only a fraction of the original's mental capacity and personality alignment.
Although seemingly not in need of protective gear akin to Vader's, the clone was adorned in a costume meticulously replicating the appearance, but lacking the functionality of Darth Vader's armor. Tash Arranda came to the conclusion that it was fashioned from leftover materials scattered around the derelict Rebel outpost on Dantooine. The clone Vader also wielded a lightsaber. However, mirroring the armor, it was a mere imitation, projecting a false blade that simply passed through objects without causing any harm.
In 0 ABY, shortly after visits from Tash Arranda, Zak Arranda, and Mammon Hoole, Darth Vader returned to the facility. He engaged and eliminated his clone in combat, briefly contemplating its nature before departing the premises.