User blog comment:Henshin1971/Fairy Tail Blog Part 5/@comment-1776824-20130319051613

There's no way that that was another side of Rogue. The "Shadow" left, meaning it was an outside phenomenon; it entered him at an unspecified point in time. Also, I also hypothesize that after Gajeel disappeared, Rogue stopped calling himself "Ryos" and started calling himself "Rogue", to symbolize that he was no longer attached to his brother-in-arms, and has, literally, "gone rogue".

I don't think that Gajeel got Iron Shadow Dragon Mode in the original timeline either. Based on that "Shadow's" shock, if it was Future Rogue, then that is most likely. It seems that Rogue and Gajeel had a good fight, but Gajeel won anyway, but not in the same way. Also, it explains why the "Shadow" possessed Rogue: he thought that it if Rogue beat Gajeel, giving Sabertooth the edge, and therefore increasing their chances of victory, then maybe the Dragons wouldn't have come.

I agree with your point about Frosch. I bet Rogue's comment about treasuring his friends comes into play: he tried to protect Frosch during the invasion, and Frosch either got hurt, and then died, or it just outright died, leading Rogue to master the art of time travel from the Book of Zeref, and travel back in time seven years. Why, I don't know. I don't have enough information to go on, but that's what I think.