So I accidentally murdered one of the Blacephalon you can catch in US. But later when I returned to the spot you are introduced to them by the Ultra Recon Squad, I encountered it again and was able to catch it this time to trade it for a Stakataka to complete my dex. This means you can just catch one for the dex and shiny hunt the other if you want or soft reset for them, at a later time. Important: I did not rechallenge the league for this to happen.
