10. At Least One Avenger Shows Up
The Rumour: At least one member of The Avengers will briefly show up in the film, serving as a tie-in for the upcoming Avengers: Infinity War.
How Likely Is It?: Tony Stark is almost immediately a no-no due to the costs attached to Robert Downey Jr, Captain America will cameo in Spider-Man: Homecoming so that seems pretty pointless, but there are compelling reasons that Thor and The Hulk could appear.
Firstly, James Gunn was snapped on set holding Mjolnir, and though he claims it was merely a spare prop, that's exactly what a filmmaker desperate to preserve the surprise would say.
Secondly, a post-credits scene featuring The Hulk would provide a neat lead-in for his appearance in Thor: Ragnarok, but at the same time it's entirely possible that Hulk's arrival in the gladiator arena in Ragnarok will be a big "wow" moment and Marvel won't want any further nods to his presence up to that point.
Basically, a tiny cameo isn't out of the question, and Thor's probably the most likely candidate, but don't get your hopes up. 3/10