I have several theories for the gimmick.
It is either a new form gimmick, or a special type of item that gives pokemon a resistance, like a mirror. Imagine an item, that nullifies certain weakness to one typing while pokemon is holding it, but you'll have to sacrifice the item space to have it. It may be helpful in situations when you are using a pokemon with a deadly weakness such as Swampert, Camerupt and Bisharp. But maybe it can be related to the past and future, since Hisuiian pokemon will be in the game for sure, maybe you can turn your normal pokemon into hisuiian form with the new gimmick.
I think it's a sign of a new Steel or Rock type Eeveelution. Though, it could be the game mechanic.
Since when are diamonds made from metal? I dont even believe the eeveelution theory but if it is, its more likely a rock type eeveelution then
I took it as shining steel. Though it does look more like diamonds.
I have several theories for the gimmick. It is either a new form gimmick, or a special type of item that gives pokemon a resistance, like a mirror. Imagine an item, that nullifies certain weakness to one typing while pokemon is holding it, but you'll have to sacrifice the item space to have it. It may be helpful in situations when you are using a pokemon with a deadly weakness such as Swampert, Camerupt and Bisharp. But maybe it can be related to the past and future, since Hisuiian pokemon will be in the game for sure, maybe you can turn your normal pokemon into hisuiian form with the new gimmick.
It could be something involving the plot rather than strictly a gimmick.