It won’t let me fight with these Pokemon on Free Battle singles, Why is this happening?

Question

I have a team of all legendary Pokémon. I have a Diancie with Diancite, Mew with Mewnium Z, Mewtwo with Mewtwonite X, Melloetta with nothing, Keldeo with Waterium Z, and Yveltal with Darknium Z. I do not understand why it won't let me battle, I even selected Special Allowed.

Comments

No I triple checked and made sure it’s free battles

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Ah right, checked myself and you can't play a rated free battle it seems. I don't know enough about the format and what the game checks for these battles so I'm not sure I can answer your question, but hopefully you'll be able to make some meaning of out of this: http://w11.zetaboards.com/Battle_Spot_Center/topic/9635696/1/
It's the official rules list for the format. Maybe you'll find something there that explains why your team isn't being accepted. It's at least highly unlikely to be a 'glitch' in a modern first-party studio game.

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If the Pokémon were hacked, then maybe the hack checker has a problem with them?

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Lol you need to change your team. A melloetta holding nothing, and the rest holding z crystals and mega stones?

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Try entering this team with only Mewtwo and Yveltal. Is the team still not allowed?

Answer 1

You didn't respond to the clarifying questions, so I'll have to answer based on my best guess.

Mythical Pokémon are considered to be special Pokémon in some, but not all, contexts.

source
So "special allowed" might have banned Mew, Keldeo, Meloetta, and Diancie. It might also have banned Mewtwo, because mega Mewtwo X is physical and not special.