Imagine a pony covered in quills or needles like a porcupine, and the pony is called Porcupone. "She's a prickly pony but she's sweet on the inside."
How about a pony with a pair of binoculars around its neck and one of those khaki caps on its head, tied under its chin with a string, and the pony is obsessed with hunting for cryptids? The little spot on its side could be the silhouette of Loch Ness Monster.
Picture a little pony whose patch really just looks like a birthmark. All the ponies that meet her think it's something different, like a Rorschach test. This pony loves having the ability to be whatever people are looking for, but at times struggles with the fact that she doesn't know what she really wants to be.
Now there is a grey pony with a white spiderweb mark on its side. Its presence first became known shortly after construction of the Glue Factory was completed, but it's not clear where it came from. This pony constantly has ants crawling across its skin and doesn't really speak. This pony only appears in the background of scenes in which there is soon to be a death of some kind.