The first Malder prototype, the "grey head" one. It has only two caps on the side of the shell, the parts of the neck are thiner, and at the place of the rear grids on the shell, there is a third opening part (it seems it is open on the second photo). It also has a double missiles gun on the front opening section (it is not easy to see, but we can notice that the panel is identical than the one on the second prototype under, and this panel is not the same at all on the actual toy). Those are the sole photos known of it. I still don't know what is inside this third opening part.
The second prototype, that was coloured purple in the begining, and with the real colours on the box art. It still has ionly two caps on the side, and the double missiles front gun, but it has the final neck, and the third opening part disappeared to let the grid that is seen on the toy after.