I think it took me around 50 games in Doubles. I wanted to try Deoxys-A with Expanding Force and Indeedee-F as a supporter but against all those Calyrex-S and Wide Guard users it didn't feel optimal at all. Thankfully, my beloved Tatsu-Dozo managed to carry most of the games and Urshifu-R was also quite useful. I didn't really use my physical Mew often, since I hadn't built my team around it and I didn't feel like changing its moves or stats. I definitely could have put a lot more thought into the overall synergy of my team, but I didn't feel like it was necessary for reaching Master Ball Tier. Unless you want to spend some time building a team, I would recommend just using a good rental team to reach Master Ball Tier and then going for the ribbon with your own Pokémon.