They're doing the kind of deal that Black and White 2 was, where you have a completely different story with (technically) a different mascot legendary. It's not like Emerald where it's the same story but Necrozma. And there were several key differences that, if you paid attention, you would notice. For example, there is a Totem Togedamaru and a Totem Lycanroc-Midday, (cont.)