Without any Jedi left to duel with, Darth Vader would often hone his skills by dueling with Training Droids such as this one. It was a droid much like this in the Shadows of the Empire comic that Vader trained with after testing the damage sustained to him by Luke Skywalker during their duel on Bespin's Cloud City.
For this custom I cut off the right arm hand of the ASP-7 Droid, glued a blue lightsaber to the stump and sculpied over a new "conduit" between the saber and arm. After that I used part of the hilt from that saber to make an "eye" for the droid and put some sculpey over the hole in the head's face plate. After that a nice liberal coat of silver paint, finished the job.