eternamaxeternatus

in this reality eternatus succeeded in the darkest day where 20,000 years later, zacian and Zamazenta are back in fighting condition, and ready to help you defeat eternatus, but the three of you know you don't stand a chance, so arceus blesses you with the rusted gun, used to summon zagurinu, a dark type and a dark steel type with the rusted gun. will this be enough to stop eternatus, or will you need the help of other legendary and mythical pokemon