Of course we all know that Human Smoke, and Masked Sub-Zero were put in the game to give the game more fighters. Here is my opinion of why there are two of each. Remember this is just my opinion so tell me what you think.

Let me start with the two Smoke's. In MK3 Smoke was introduced as a cyber ninja. In his ending in MK3 we learn that of all the cyborgs, he still had a soul of his own. Now in MK: Deception Smoke is in both forms for us. My opinion is this: Human Smoke and cyber Smoke can co-exist becuase he still has a soul and his soul can escape his artificial body (hence the MK3 ending) whenever he wishes. He can also return to his cybernetic body whenever he wishes, so in UMK3 and MKT both Smoke's can be in the same arena and fight if they want.

Now onto the two Sub-Zero's. The unmasked Sub-Zero is the younger Sub-Zero of course. We also know that Noob Saibot is the elder Sub-Zero or the masked Sub-Zero. In the masked Sub-Zero's ending we learned that someone else was posing as the Lin Kuei warrior himself and that this warrior had previously been absent from every MK game and would return in the 4th. So in my opinion, whoever was masked Sub-Zero was in UMK3 and MKT is one of the newer fighters in MK4 or MKG. When we look at every single new fighter, Shinnok could be the only possible solution. He could possess any fighter's special abilities and he looked normal enough.

That is why I believe that there are two of each. Of course everyone knows the real reasons why they are in the game. They are there as cannon appearances. Above is just my opinion of why there could possibly be two in the game at the same time of each.