I agree with the above post that Protean Greninja and Aegislash should be banned, both to support challengers and leaders alike. Protean Greninja, for one, is capable of destroying teams with its wide pool of coverage moves, and even if it is frail, it can still damage teams before going down. This pokemon is highly advantageous for leaders as they can exploit their knowledge of the trainer's team so as to cripple the challenger heavily whereas in the case of challengers, they can use Greninja to cover several leaders due to its coverage. Aegislash, on the other hand, is also hard to deal with due to its ability Stance Change, which when combined with the right moves and the right items could prove to be hard to deal with in all formats, such as in Triples with the presence or Wide Guard, while in Singles, it can punish physical mons with King's Shield, while also making it difficult for special mons to deal with it. Thus, I support banning those mons for the sake of a better challenge for leaders and challengers alike.