Sinnoh is a region up in the north, too far away for us to likely ever go there without a concerted effort. There are many legends related to it, though everything I've found was in Ecruteak, and thus is secondhand. That's not the point, though.

Among those legends, there are two that catch my attention. The first is a group of three, not entirely dissimilar to the three beasts of Johto but on a far grander scale. One is probably irrelevant, but the other two... they're said to control time and space.