Urshifu-Base (Single Strike) was restricted from holding Mega Stones in vanilla Mix and Mega yesterday. Due to STAB and Mega paralleling vanilla MnM rules and this being a change of rounds, the restriction has been accepted into SnM and should now be effective in all environments. So please be aware that Urshifu Single Strike can no longer mega-evolve in STAB n Mega.
Thanks to Roldski32 for noticing this!