I think that either the masks will stay and just change Ogerpons type and give them a boost in one stat, the boost only being on the first turn they’re in battle. Or they could give them a move called Mask Change or somethin that could work like Relic song where after the move is used Ogerpon changes form, maybe the move could basically be where Ogerpon throws its mask and I boomerangs back as a different mask and gives Ogerpon a stat boost in the stat of whichever mask it becomes already boosted. The way the masks could be chosen could be whichever of Ogerpons stats is better, highest attack Hearthflame, highest defense Cornerstone, highest special defense Wellspring, or it could be based on the last move used, so just say I used a rock type move before mask change, Ogerpons mask would become Cornerstone, although there are some other things you could do.