Pokemon transferred from Pokemon X, Y, Omega Ruby and Alpha Sapphire will be usable in Rating Battles in Pokemon Sun and Moon. In particular, you’ll be able to use them in Single and Double Battle modes. However, regardless of where they come from, special Pokemon cannot participate in Rating Battles. Your Battle Team must also not contain duplicate Pokemon or duplicate held items. In addition, Special Battles and Pokemon World Championships Battles have different regulations for each season.
Source: Serebii
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