Weren't muscle casted from the same molds as kinkeshi? Mapman kinkeshi didn't have the cap. You don't see why someone would do this post production? lol. Have you seen some of the 100,000 painted, cut, kit bashed monstrosities that people have created with post production figures. It's nothing more than a messed up figure.
No I really don't. I have seen thousands of monstrosities but I wouldn't group this figure with those that are painted, cut, chewed up etc. With that single photo it looks like the top of the "plug" is wider than the hole in which it is capping. Meaning someone would have had to remove the top of the head to make the hole and then create the plug separately to fit from a different figure. And then glue just the bottom of it so it stayed in place. If this is the case it would have taken a little bit of effort. I just don't see what the incentive would be. It doesn't look that messed up to me but rather clean. Personally I don't think that it makes the figure that different. So why would someone take the time and effort to create a figure with a plug that essentially looks the same. And not a plug that was removable or entirely glued in but just enough so you couldn't remove it.
If it is simply a circular cut into the top of the head then it wouldn't be that strange to me but that is not what it appears to be.
