We talk about leverage here a lot and that Fox have the X-Men and FF rights, but I think there is still at least one other Marvel film right that Fox have, Deadpool. Now if you go in the X-Men forum they will tell you till they are blue in the face that Deadpool is part of the X-Men film rights, but the evidence would seem to indicate otherwise. For a start Deadpool was not a part of the original deal Marvel made with Fox, back in 2003 the film rights were held by New Line who were trying to get a film made with it but it ultimately fell through. What happened next we don't know except that the rights eventually ended up at Fox who used him in their X-Men Origins: Wolverine film in 2009.
The question then is how did that happen, one idea would be that the character's rights were absorbed into the X-Men rights but I don't see Marvel letting that happen, their deal with Fox for the X-Men rights was a mess and they let themselves get screwed so I don't think they would want to let other seperate character rights get added to it without some sort of renegotiation. And that is not something Fox would do. So the character is still likely to be under a seperate rights deal, which might be why last year Hitfix mentioned that there was a rumour that is Fox didn't use the character the rights would revert.
So that would mean that Deadpool's appearance in XMO:W was a crossover, but what sort of arrangement was made to allow that to happen. If the deal was open ended and let Fox crossover whenever they want then we can expect to have Deadpool thrown into X-Men Apocalypse in order to renew that rights and that will be that. However if the deal was just for the film then it does give Marvel a bit of leverage.
If it was a deal just for the one film then Fox have till about May 2016 to get a Deadpool film made, but with no crossover deal to let Fox tie the film into their X-Men films. For a few years Fox has said they are going to make a Deadpool film, they have a script, director, lead actor, they even say they can make it for $50million, but Fox still haven't got ahead with it. I think the problem is with no X-Men link they are stuck with an R rated film adaption of a comic book character, and that is not a type of film that had much (actually any) success. Comic book characters that have had R rated film adaptions are Judge Dredd, Spawn and Punisher, none of whom were successful, infact most can be called complete flops. So this leaves Fox with a problem, to hold onto the character they would have to make a film that stands a very high chance of flopping (the last Punisher film made $10 million and cost $35million). So how much do they want to hold onto the character?
If Fox could throw him into an X-Men film then they wouldn't have to worry. So that gives Marvel something else they can use in any negotiations, nothing big but every little thing helps.
(btw sorry this ended up so long

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