Here's what we knew before this two-minute trailer for X-Men: Days of Future Past: it's based on the comic arc of the same name, Wolverine is going back in time to prevent a dystopian future for mutants, and it will be split between the present day and the older world of X-Men: First Class. This teaser doesn't necessarily shed more light on the plot, but it emphasizes the pathos of a cross-generational attempt to avert disaster, and it suggests that we'll be seeing a lot from just about every major mutant from either generation — including Michael Fassbender and Ian McKellen as Magneto.