How do Fairy, Steel, Dragon cores work in doubles champions (Reg M-A)?

Question

I hear people talking about them but why?

Comments

I don’t know what this question is

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It's about building your team around a Dragon type, a Fairy type, and a Steel type, as their types have no shared weaknesses

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really thats it?

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No, there's more ways that they complement each other, but I have never been a teambuilding master, so I can't say what they are

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What format/rules are you asking about? VGC, BSS, OU, or something else?

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Will the answer depend on which Pokemon are legal? The question seems to me just to be asking what qualities of those types mean they form a good core for a team.

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It does depend on whether it's singles or doubles.

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thx sumwun

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So what format/rules are you asking about?