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If both are good partners, use "both Urshifu formes". It just can't be Urshifu with no modifier. Also, I saw you corrected a previous correction to Urshifu-S to just Urshifu- use Urshifu-S, same principle.
1/1, GP Team done
Crediting zinnias too. For future reference, when you're implementing a GP check, the best way is to use the reply method as seen in this post to make things quick and avoid eyeballing- there were a few mistakes in implementation.