R4-D6 can be seen in the background behind Luke when he tells Han to screw off in the Yavin Hangar just before the battle.  Allegedly, this droid is the same exact prop used for R4-I9, which was stationed on the Death Star.  Hasbro gave us that droid already, but it was painted black instead of this proper midnight blue.  Basically, you could have two of these, and decide that one of them is a proper R4-I9.  You had two chances to build this droid.  Once with 4 mainline figures, and a second time by acquiring the 4 figure “Greatest Hits” subline.  This was basically the very first build-a-droid figure you could make, if you put them together based on the numbering of the figures which included these parts.

I particularly like the R4 droids.  I’ve always though the cone-shaped heads were neat.  It was a real treat when we finally got R4-M9.  This one is also pretty cool, and you sort of get a two-fer, since it’s really the same as R4-I9.  The issues with the mold here are the soft plastic used for the legs (some of my BADs have warped a bit over time) and the second set of “leg” holes at the bottom of the body.  It was obviously intended to give additional weird options for droid variations, but later for that noise.  What are we, a bunch of kids who have to use our imaginations?

Source:  A New Hope.

What you need to build R4-D6:

BD3 Chewbacca

GH3 Battle Damaged Darth Vader

BD4 Leektar & Nippett

GH4 EVO Trooper

BD1 Han Solo

GH1 Commander Gree

BD2 Luke Skywalker

GH2 Kashyyyk Trooper