This could be common knowledge to a lot of people, but it's still pretty complext. I also don't own the game but have read most of the spoilers. And in Sindel's ending we see that Onaga is released from his shell, finding the human form of Reptile. (Which got me thinking) Since UMK3 we've seen the de-evolution of Reptile, from ninja, to human-like lizard, to Godzilla's baby brother. Now, in the intro of Mortal Kombat Deception Shujinko clearly says the "prophecy" had come true, Onaga the Dragon King had returned. I think this clearly states why Reptile has been de-evolving, his body was growing more animalistic to be a fitting shell for the spirit of the Dragon King, fulfiling the prophecy, hence why we see the ninja form of Reptile once Sindel defeats Onaga. Like I said, when you think about it, it's seems simple. Also I haven't played so, there is a chance Konquest could prove me wrong. I'm pretty sure this is what the MK team had i mind with Reptile too, but ehy I can't read minds, it just seemed sensible. You guys argee, disagree?