After hearing comments for and against, I've decided not to use the ribcage. I also did some action sketches (I'll post them later) and felt like the ribcage really got in the way. If that's the case with pencil sketching at unlimited size, then I can only imagine the problems for spriting. Here's the "final sketch", with minor updates to the hands:
I also have a background story for this pokemon. While the tale below is generally considered a legend, I have it on good authority that it is based on the actual facts behind the origin of the Steel Ghost. Take it for what it's worth...
The Fable of the Steel Ghost:
A Bedtime Story for Young Trainers
Once upon a time, there was a great scientist that worked in the field of robotics. His goal was to create a completely artificial pokemon. He built a lab in one of the most remote areas of Sinnoh, to conduct his research in total privacy. If he succeeded, he planned to give his creation away and make a valuable contribution to all the pokemon trainers of the world.
Very quickly, the scientist was able to create a strong battling machine. He even created new synthetic materials that would "grow" over time, becoming stronger and more complex as time passed. The scientist made a robot from these materials, and covered it in a pseudo-organic skin. The result was a synthetic pokemon that looked exactly like a real living organism.
Unfortunately, despite all the mechanical features and electronic capabilities the robot possessed -- it lacked the battle spirit of a real pokemon. It had no soul. Without a soul, the machine was regularly bested in battle by other pokemon, who are trained from the moment they are hatched, to find a way to win in fierce, hard-fought battles.
To overcome this shortcoming, the scientist immersed himself in cutting-edge artificial intelligence technology, with a single-minded goal to create a synthetic soul for the robot pokemon, to enable it to battle with the zest and vigor of a real pokemon. After years of research and experimentation, the scientist finally achieved his goal. He succeeded in making a cybernetic pokemon with true artificial intelligence.
The robot could not be programmed outright, like other machines. It had to be trained, just like a real pokemon. But, when trained, the robot was immensely powerful. Its battle spirit was so ferocious, it would rush headlong into every battle and quickly destroy the opponent.
The scientist's creation was so lifelike, he discovered he could even breed his creation with Ditto -- whose amazing breeding powers enabled it to duplicate the base material of the robot perfectly. The scientist bred and trained dozens of synthetic pokemon, each one as fierce and aggressive as the next one. Convinced that he had made the perfect artificial battling pokemon, the scientist prepared to announce his creation to the world.
Unbeknown to him, the scientist's work was being secretly monitored by Team Galactic. Fearing that the new robot pokemon would foil their plans for world domination, Team Galactic ambushed the scientist's lab. Inside the lab, they opened a dimensional rift and destroyed everything they could find by throwing it into the rift.
The scientist tried to stop the members of Team Galactic by unleashing his army of robot pokemon. Unfortunately, the robots were so impetuous and bloodthirsty for battle -- they flung themselves headlong towards Team Galactic, and were swallowed, one by one, into the dimensional rift. Even after many of the robots had destroyed themselves, the rest continued to follow, like lemmings off a cliff. The scientist had been so determined to make an aggressive pokemon, that he neglected to give the synthetic pokemon any sense of caution. As such, the robot pokemon were all quickly consumed by the rift.
Seeing his life's work completely destroyed, with nothing left to live for, the scientist sacrificed himself into the rift as well. With the lab and artificial pokemon destroyed, Team Galactic left and continued their nefarious plans to take over the world.
But something strange happened after that. No one knows exactly why, but a new species of pokemon mysteriously popped into existence. Apparently the scientist was even more successful than he originally thought. He had created such a perfect artificial "soul", that the spirits of the destroyed robot pokemon re-emerged as ghosts! They were no longer covered in synthetic skin; they appeared as animated steel-like skeletal structures. But they possessed all the battle abilities they did before, plus some new mystical powers as well. These new undead robot pokemon were able to breed with the Dittos in the lab, and eventually flourished in the remote area of Sinnoh surrounding the lab.
Years later, the ghost robots were discovered by wandering trainers, who captured them and used them in battle. The robot ghosts apparently learned something new after being caught by surprise and exterminated as a result of their impudence. Unlike their previous ancestors, the robot ghosts were particularly cautious in battle and always on the outlook for trouble and lurking surprises.
Word quickly spread of this amazing new species and their incredible skill for discovering details about their opponent in battle. These ghostly steel skeletons are now prized by expert trainers everywhere, for their unparalleled proficiency at scouting -- the species is often referred to as "The Ultimate Scout".
In the end, through hard work and a tragic sacrifice, the scientist inadvertently succeeded in making a valuable contribution to pokemon trainers around the world.