It seems that most people are set on the idea that if there is another character it's Noob Saibot. Why is that? I have a different theory (and it's JUST a theory), a few people have said the "code" to unlock the secret is a combo...so what if the hidden character was Sektor and you had to do Cyrax's Ketchup combo on a certain screen. Remember the story of how Sektor and Cyrax were called Ketchup and Mustard when they were first created, (the story is in one of the Koffins). Anyway, just a thought for the sake of thinking.