They usually serve as an omen, don't they? In a lot of the gothic and folk horror stuff I've read, a skeleton deer isn't just a spooky aesthetic prop. It's a boundary-crosser. Its form takes something associated with gentle wildness—a deer—and strips it down to the stark, unforgiving architecture of bones. That contradiction is where the magic (or the horror) happens. It becomes a messenger from a realm where life and death aren't separate states but are woven together.
I'm thinking of stories like 'The Only Good Indians' by Stephen Graham Jones, which plays with deer imagery in incredibly potent ways, though not exactly a skeletal one. The skeleton version would amplify that. It could be a guardian spirit of a cursed forest, a physical manifestation of a land's memory where all the flesh has been scoured away by time or tragedy. In romantic dark fantasy, I've seen it used as a familiar for a lich or a sorrowful necromancer, a beautiful, silent companion that underscores their connection to decay without the visceral gore of a rotting corpse. It's a cleaner, more elegant kind of death symbol, which can be strangely poignant.
In some webserials I've dabbled in, they appear as quest-givers or guides. You follow the pale gleam of antlers through a misty wood, and it leads you not to a clearing, but to a threshold. The role is less about direct action and more about direction, a signpost written in bones. It's rarely just a monster to fight; it's an embodiment of a theme, which makes it stick with you longer than some generic ghoul.