Scientific Name: Hypomyces lactifluorum
Common Name: Lobster Mushroom
Certainty: positive (notes)
Location: Southern Appalachians; Smokies; CabinCove
The name is misleading: it is actually just (admittedly colorful) mold growing on top of some poor hapless malformed mushroom. In fact the host is so badly developed it can be impossible to identify. Fortunately this particular species of mold only grows on edible mushrooms, because it is highly-esteemed by those who esteem this sort of thing.