Expect the only pokemon that has 600+ BST and is allowed on the mason are the Pseudo-Legedaries and Slaking.
I made a post explaining what I define as Legendary pokemon, as well as the Mythical subset and the Outside Pseudo group. I'll bring it up once I find it
While Slaking at least has an Ability holding it back, mechanic-wise what makes a pseudo legendary allowed but a Legendary with +600 not? Not to mention the VGC and Maison allows Mega Evolutions which boosts a Pokemon's BST above 600 or at least gives them something that makes them as stronger if not stronger than a Legendary. Also honestly I'd only label a few of the Legendaries with a BST of 600 overpowered: Mew (it can learn any move), Deoxys (of course it does come with major drawbacks, but still it can become a sweeper once set up), Darkrai (speedy attacker and Dark Void), Shaymin Sky Forme (speedy attacker and Serene Grace Air Slash), and Victini (though only if it has V-Create to NUKE EVERYTHING). All the others seem fair game to me, at least as fair as the Pseudo Legendaries and Mega Evolution. Honestly I think the Battle Maison (or facilities like it such as the Tower and Subway) need a bit of a revamp. They should really have multiple rule sets for what Pokemon you can use. No Legendaries & No Mega Evolutions, No Legendaries & Mega Evolutions, 600 BST Legendaries Allowed & No Mega Evolutions, 600 BST Legendaries Allowed & Mega Evolutions, Everyone Allowed, Only Legendaries Allowed, etc.. We now have so many Pokemon that I don't think this is out of the question and to some extent now needed.
