Unfortunately, it's not uncommon for major spoilers from games and movies to leak out before the debut, something we have recently seen with Resident Evil Requiem, for example. People seek attention on social media without considering that they are also spoiling the fun for countless others.
But sometimes it's harder to avoid spoilers, especially when official sources are leaking information. The description of the upcoming The Super Mario Galaxy Movie is now guilty of this. IGN reports that the British cinema chain Everyman has unsentimentally posted the following presentation (one last warning: don't read on if you want to avoid spoilers!):
"After defeating Bowser and saving Brooklyn, Mario faces Wario and Bowser Jr.'s evil alliance. Now, alongside his friends and Yoshi, he must stop their plans for world domination."
In short, Mario will not only have to battle Bowser Jr. but also Wario... a character who has been kept secret until now. We assume that he will play a fairly significant role as one of the villains in the film, and the fact that Nintendo has not mentioned anything about this suggests that they intended for cinema-goers to discover this for themselves.
It's possible that this is a mistake, but it seems unlikely that a cinema company would write a description and simply make up claims about a character. What do you think about Wario appearing in the film?