I was thinking about the Smoke Monster and I remembered the episode where Ben summoned The Smoke Monster to kill Keamy's group after they killed Alex("The Shape of Things to Come"). After watching that episode it looked to me like Ben could call on/control Smokey. He didn't even really LOOK scared. When he saw Flocke as the smoke monster he looked a little shook up. It makes me wonder whether or not the MIB is ACTUALLY the smoke monster or just taking on the smoke monster's form like he did with Locke and Christian etc.
I also think that there maybe another smoke monster that's white. Locke saw it in "Walkabout" and said "I've looked into the eye of this Island... and what I saw was beautiful." However, in "The Cost of Living", Locke would later claim that the entity he saw was not the black smoke but rather a "beautiful bright light," suggesting that he saw a different form of the Man in Black or a completely different entity entirely. I think that this may be Jacob.
In the episode "Exodus, Part 3" Locke was convinced that the smoke monster wouldn't harm him like it didn't before but After his past encounter with the "Monster", Locke was confident he would not be harmed and decided to approach it instead of running away. However, this time he did attack Locke and knocked him to the ground. After looking up in horror, Locke stood and started running frantically. He was then "grabbed" by the smoke and dragged across the ground by his left foot. Jack was able to grab Locke by the arms as the Monster attempted to pull Locke into a hole in the ground. The black smoke was visible around Locke's ankle as he was being pulled into the hole. Locke told Jack that everything would be all right and told him to let him go. But Jack refused, ordering Kate to get the dynamite from his backpack and throw it down the hole. When she did so, there was a large explosion and Locke was released. The cloud of smoke was then seen dissipating as it retreated from! the group(http://lostpedia.wikia.com/wiki/The_smoke_monster). I think that this was the first time that Locke came into contact with The Smoke Monster/Black Smoke. Now whether or not it was a different smoke monster or the MIB as the smoke monster, I am not sure.
Even after seeing the MIB see his reflection in a window I am still not convinced that the MIB is actually the smoke monster. To summarize, I feel that he has just taken on it's form to travel and harm/kill people that are in his way. Because why would the MIB let Ben control him?