The Amazing Spider-Man 2 is already out in theaters overseas, and kicks of the summer blockbuster season in in North America this Friday. While the buzz surrounding the return of Andrew Garfield's Peter Parker has focused heavily on the roster of villains that the sequel introduces, there are even more sinister characters that the studio hints at during the credits at the end of the film - although it's not something you'll see on the big screen.

In an interesting spin on cross-studio marketing, we learned (and confirmed through Sony) that there is in fact a mid-credits "button" in The Amazing Spider-Man 2, but it surprisingly doesn't tease anything upcoming from the Spider-Man universe, or anything from Sony Pictures for that matter. Instead, the time is taken to showcase a clip from X-Men: Days of Future Past, another Marvel-branded project, but one from rival studio Twentieth Century Fox. That was part of a deal between Fox and Sony that involved Fox bending their contract with director Marc Webb in order to let him direct the Spidey sequel in exchange for some free X-Men marketing.

*** Warning: Minor Spoilers Ahead ***

Fans looking forward to a teaser for the story or villains for 2016's The Amazing Spider-Man 3 or the confirmed spinoffs in development for Venom and Sinister Six are not entirely out of luck though. Take a look at this interesting message from Sony:

After seeing THE AMAZING SPIDER-MAN 2 – opening on May 2nd - be sure to Shazam the end credit sequence to unlock a look into the sinister future.  Download @Shazam on iTunes or GooglePlay. #SpiderMan

Specifically, use the Shazam app while the song "It's On Again" (Alicia Keys feat. Kendrick Lamar) is playing for a special surprise music video. Note the word usage ("sinister future") in the official statement above. You can try it from home with Shazam during the official music video (hat-tip to Coming Soon for coming up with the idea):

When you do, this will pop up and you can click the top 'Play' button to see the teaser.

The Amazing Spider-Man 2 Shazam Viral

The animated video features blueprints and concept designs of the Oscorp tech behind what seemingly may be the six core characters on the Sinister Six roster. We grabbed the following screenshots from the video so let's take a look and try to determine who might be in the film:

[gallery columns="1" ids="447491,447492,447493,447494,447495,447496"]

Judging by the images, we can clearly pick out the Goblin Glider so that's probably Dane DeHaan's Green Goblin (or Hobgoblin?). Doctor Octopus's mechanical arms and Vulture's wings are obvious. The other ones seemingly highlight Rhino's mechanical tusk so expect Paul Giamatti to return (he hinted as much before) and the symbol of Kraven the Hunter (worn on his classic Marvel Comics costume). Last but not least, we can't confirm the sixth. Some speculate that it could be Mysterio, Shocker or Chameleon but since the team will deviate from the books, there's a chance it could be Black Cat - adding some much needed femme fatale flavor to the villainous army. It's something our own Kofi Outlaw speculated upon last week and Felicia Hardy does have a small part to play in The Amazing Spider-Man 2.

What we do know about Sinister Six is that Drew Goddard (Cabin in the Woods) is helming it and that it is planned to release before 2018 (when the fourth core Amazing Spider-Man will release). Producer Matt Tolmach recently went on record explaining that "nothing is sacred" in terms of the roster combination, only that the film version will be the "best six" imaginable, a group that'll make sense in the universe being established in The Amazing Spider-Man 2 and followups.

Roberto Orci Talks Sinister Six and Venom Movies

Despite the exciting reveal images releases, The Wrap claims that the final six have yet to be finalized for the studio, which goes a little bit against what Tolmach said recently. Perhaps it's that uncertainty being why the sixth image can go several different ways. They also learned that production on Sinister Six could begin in Janurary 2015 which would point towards a 2016 release. Could we get to Spider-Man universe movies in 2016 alongside Fox's X-Men: Apocalypse and two movies from Marvel Studios?

In the meantime, for your first look at the beginnings of the Sinister Six, check out The Amazing Spider-Man 2. As for this little marketing ploy, it's certainly a unique and innovative viral technique. There's also of course the little problem of theater-goers having to have their phones on ready to go at the end of the film in order to Shazam during the audio clip. Not that it matters during the credits.

At the very least, this example will get studios thinking of other similar and new ways to take advantage of the post-credits teaser trend, something that Marvel Studios has made  a business out of in orchestrating its cinematic universe, the blueprint Sony - along with Fox and Warner Bros. - are going to be embracing as well.

Who do you want to see in Sinister Six? Let us know your thoughts in the comments!

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More: Passing The 'Spider-Man' Torch To Miles Morales

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The Amazing Spider-Man 2 is directed by Marc Webb and stars Andrew Garfield, Emma Stone, Jamie Foxx, Dane DeHaan, Colm Feore, Felicity Jones, Paul Giamatti, Sally Field, B.J. Novak, Marton Csokas and Chris Cooper.

The Amazing Spider-Man 2 opens in theaters on May 2, 2014, The Amazing Spider-Man 3 on June 10, 2016, The Amazing Spider-Man 4 (no official date or title) in 2018. Sinister Six and Venom do not yet have release dates.

Follow Rob on Twitter @rob_keyes.

Source: CS, Sony, The Wrap