Mewtwo

Thanks to Mewtwo's massive Special Attack, Speed, and coverage movepool, it is a very good wallbreaker in Ubers, capable of taking on many staples of the tier like Eternatus and Zygarde. Despite facing competition as a fast special attacker from Calyrex-S, Mewtwo has a far better movepool, isn't reliably checked by the most common answer to Calyrex-S in Yveltal, and can actually synergize well with Calyrex-S because both break down their shared checks, such as Zarude, Ho-Oh, and Yveltal itself. However, Mewtwo is always forced out by Calyrex-S and offers very little defensively, which makes it hard to fit onto teams and bring in repeatedly throughout a game. Mewtwo can also be difficult to make the most of because it can be quite reliant on prediction, and getting a turn wrong can result in Mewtwo being crippled.