From one of the newer 2019 plushes to one of the older modern types, here's an example of an aged Kelly Toy Super Sonic. They used the shiny gold fabric for him, and this is what can happen as it ages. The shiny-ness is some kind of super thin or fine plastic, and it somehow goes bad/gets brittle/ something happens as it ages and it turns to dust and flakes away, leaving a kind of grubby gray surface behind. This fabric isn't uncommon, either, and it's sure not exclusive to this doll.

Other toys/plushes or accessories made with it can all have this effect. But because the whole doll was made this way, it's especially obvious here. Notice the inset, that's the texture it gets. Then, some of these were created smiling normally (SS is generally shown frowning or determined), which is the case for this doll.