>>36653890BW because Reshiran and Zekrom
B2W2 because Kyurem-White and Kyurem-Black
SM because Solgaleo and Lunala
USUM because Necrozma-Dusk Mane and Necrozma-Dawn Wings
but
Emerald because of Rayquaza
Platinum because of Giratina
it's obvious that it's going to be named Z or something related and not any X2Y2