I don't believe that the Ven we've seen is the actual Ven. I think that DS is the real Ven. I think it was possible that the real Ven went under the guidence of Master Xehanort, but he became out of control and used his darkness to gain more power. I believe that when MX said "That man is a monster infused with darkness. Correct my mistake" he was talking to fake Ven about DS (real Ven). I think he cloned Ven, and that's who we have been seeing. OR it's possible that MX was talking to Terra about DS, because Terra was heading down the same road as he was, but turning to the darkness in his heart. When MX approached Ven in Olympus Coliseum, MX asked if he remembered him, and Ven had no idea who he was. When DS attacks Ven, it's prolly because that he wants to kill his clone. I think Ven discovers that he is not actually him throughout the game, and that's why he asked Aqua to "erase" him. I don't think Terra or Aqua understands anything about it. This theory also explains that I don't believe that MX is completely evil, but DS (real Ven) is the one who is actually evil.The reason why I cam up with this is because DS and Ven have a very similar body figure, and some of the things that Ven and MX say sort of makes me think this even more.