We all love certain characters and would do almost anything to see them again, but, like the Good Book says, sometimes they come back wrong. Sometimes the characters you love are shoved into a new film like a toddler cramming toys up his nose.
Look, making movies is a notoriously hard thing. Most of them cost millions and millions of dollars, and that's just the marketing. One of the best things to throw in your marketing is an A-list actor or a returning character from the previous film - bonus points for both.
Because of that, a lot of films that have no real reason will bring back a beloved character from the past, even if it makes no sense, is forced, and has no effect on the story. Hey, at least it gets people into theatres.
10. Ra's Al Ghul - The Dark Knight Rises
Ra's al Ghul, the Demon's Head, is one of Batman's fiercest foes. In the comics, he cannot die, but is risen eternal through the dread magic pool of green slime, the Lazarus Pit. So when he died at the beginning and end of Batman Begins, some folks thought that he might be, actually, immortal. (Sure, Bruce says it's just a clever ruse, but Bruce also thought Ra's was Ducard, so his Detective level isn't real high, surprisingly.)
Rumors began flowing that Ra's would return in The Dark Knight Rises, with his League of Shadows being the main villains of the film. He would come back, having been revived in the pit, back to face down Batman one last time.
But that wasn't true. Ra's was dead. Not that that stopped him appearing.
Almost as if to make fans not feel disappointed, Ra's appears for a brief moment in The Dark Knight Rises, as a hallucination. It's like the film was finished and audiences kept expecting Ra's to turn up so they added this film in the reshoots. It's forced and pointless, just like Christian Bale's growl.