Okay, here is an example:
George and Fred play each other in a tournament match.
George picks Harry Potter and Fred picks Voldemort.
Fred Slaughters George.
Fred stays as Voldemort.
George decides to go with Dumbledore, his secondary, who has a good MU against Voldemort.
Fred bans Hogwarts, since he lacks a decent projectile and sucks there.
Dumbledort than selects Platform nine and three quarters, because he has a chaingrab that works on Voldemort there for up to 90%. Also, the layout of the stage aside form the two walls were Dumbledort can CG is very similar to Hogwarts as it favors camping and is long and has no platforms. In the standard ruleset, Fred could switch out his character, so he could have more of an advantage. That's were your rulesets differ. In yours, Fred is stuck on his second worst stage where Dumbledore, George's character, has a great advantage on him there. In the current ruleset, Fred can now pick Grindelwald, who has a heavy matchup advantage on Dumbledore under normal circumstances. George know switches to ALberforth, his other secondary, who lacks Dumbledore's CG but has a good matchup against Gellert ( Grindelwald. )Fred stays the same as he is confident he could beat George even now.
Please replace all Harry Potter terms with Brawl terms on your own.