Here we see Batman's arch nemesis in prototype form. This protomolded figure is entirely hand painted as the title mentions. I find hand detailing lends any prototype a much more brilliant appearance than the production counterpart. Notice the right hand lacks the hole for the Joker Mallet.
Protomolded figures were created in house at Kenner using low yield aluminum molds. One distinguishing characteristic is the milky white plastic employed in their creation. They never possess dates, copyright information, or footholes. These prototypes were specifically used as paint masters, catalog/photography samples, and trade show display pieces. Based on noticeable paint loss on the feet bottoms, I'd put the use of this prototype in one of the last two categories described above. Obviously the figure was glued down to something at one point.
The above picture provides a comparison with the production figure. The prototype stands on the right, while the production figure stands on the left. Side by side, the prototype's brilliant hand detail is strikingly evident. If you look extremely closely you'll notice the prototype's jaw is much less pronounced. Kenner probably altered the head sculpt at some point, which explains the difference. Another minuscule difference is the prototype's lack of black paint inside the mouth. This prototype surfaced in a large find which included many Super Powers and Star Wars prototypes. The collection was consigned for an ex-Kenner employee by a well respected toy dealer in Cincinnati. This same find yielded all but one of the paintmaster figures with paint swatches showcased on this site.