I decided to save my gems ’til the banners of sygna suit Blue, which at the moment seems like it’s never coming but due to that, I didn’t use any gems to pull Serena, and this was the method I came up with to clear Cobalion without her.
If you time it right and if you’re lucky enough, you can finish with these trios without any faints.
Every necessary info is on the video, but I’ll just write down the sync pairs I used :
-Gengar (lucky skill : Troublemaker 1)
-Torkoal 3/5 (Vigilance)
-SS Red’s Charizard 2/5 (Critical strike 2)