Well, I went right to the source, Packrat Studios, and found out which base figure this is. It's a McFarlane Solidus Snake. I've begun work on my own iteration, and dang, it's not simple. The Solidus figure appears to have a double knee joint. It does not. In order to maintain the double knee articulation, I've had to dremel out the interior of the Solidus upper leg and whittle down the Apocalypse upper to fit inside. It's not quite done, but I think it will work. Also, the chest features some holes that need to be filled in, and you can see that both unknown and Packrat have done such a smooth job doing so that I wasn't aware of it until I got the figure in hand.
Here's the original from which we are both copying:
http://packratstudios.blogspot.com/search?q=apocalypseI'm going to attempt to do the shape-shift accessories using the inherent Robotix connectors instead of magnets like Packrat's original. I'll let you know how that works out, it may be quite a while before I get back to it. I'm not sure where to get something like the mace he has. Any ideas?
I'm also cursed with a Solidus base figure that seems to come from a home wherein smoking was enjoyed with an enthusiastic religious fervor. The thing just smells bad. Any thoughts on how I can remove the odor?