Like for instance we all knew Ash's Infernape would be the one to take down Paul's Electivire since it has been hinted so many times that they had a rivalry.I think Ash's Mijumaru will be the one to have a rivalry since Shooti's Tsutarja has a type advantage.Though a part of me believes it's going to be Pokabu since it's usually Ash's fire starter that beat's the rival in the league examples Charizard and Infernape.