During Stephen Amell's Salt Lake City Comic Con panel, he shared some interesting info about the show's 50th episode. Said Amell-
"Last night, I watched the director's cut for episode 304 and it was awesome. It is our 50th episode, it is worthy of a 50th episode. It has a scene and a confrontation in it that has literally been 2.5 years in the making."
When the title of this particular episode was announced, ("The Magician") it was immediately speculated that the show could be introducing Zatanna or some other magical DC Comics character. But executive producer Marc Guggenheim quickly dissuaded that notion, clarifying that the title refers to John Barrowman's Malcolm Merlyn, who is currently presumed dead by most of the characters on the show. One, long-running plot point throughout Arrow has been what happened to Malcolm when he went to Nanda Parbat to train with the League of Assassins and how he escaped thier ranks to carry out his nefarious plan during Season One. Given the way Barrowman's character has tensed up during the last two seasons at the mere mention of Ra's Al Ghul and the "League", it's probably safe to assume that he didn't leave Nanda Parbat on good terms with Ra's.