It is interesting with these lights and darknesses. According to MX, he needs both sets to complete his goals. If he has all 13 darknesses but not all seven lights, he still can't create the X-Blade. So, while the lights are his enemies, he needs them alive or otherwise to complete his plans.
Now, this is all assumign those translations in that video are accurate (rambling time, folks):
From the video, he was apparently going to maybe make Sora the 13th Darkness. The problem there is that would take away one of the Lights, wouldn't it (if you need 20 actual existences or if you can double up and have one person be both a light and dark). And Mx's words appear to say that he has both Sora and the final Light (or, the Light that wasn't accounted for). The dialog has Mickey saying 'The last one' and then MX also says 'last one,' so we can assume that MX is referring to the last Light. The three missing seems to infer Ven, Aqua and Terra. however, when MX points out that three are missing, he then says that the lights are chosen naturally. That makes it sound like the 3 Lights haven't been made apparent yet and it might NOT be Ven, Aqua and Terra.
Assuming that the three lights are TAV, then it is strange. MX says he has the last light and if the other 3 are TAV, then MX doesn't have Terra at the moment, otherwise he would have said that he had the last one plus one of the missing lights.
Interesting to note that MX says he has Sora and the last Light. However, when he is about to make the 13 Darkness, he never actually says Sora. Of course, we see Sora being lifted in the chair about to be Xehanorfied. So either Sora was going to be the final Darkness and be a light at the same time or MX was aiming for someone else in Sora to make a darkness instead, like maybe Roxas (assuming the intro is non-canon). The way MX worded his sentences, it leads me to believe that he doesn't know that Sora has Ven's heart.
The last one is on their side as MX puts it, so maybe it isn't Kairi or Lea as the final Light (or if Lea really was a double agent again and always working for MX). The last Light could be Roxas, which would fit with MX's words and since he knows that Roxas returned to Sora. however, I'm going to say a crazy idea and throw out something not thought of yet: what if the final Light which MX's holds and could possibly have gotten considering where his heart was actually Eraqus?