I think once I was scrolling through eBay and found a 2nd wave Seapony that looked almost perfect. I clicked to look at it and her one side was okay...then I saw her other side which was completely brown and sunken in from mold I believe. If I'm remembering right I also once saw I think an Applejack who looked like she had been thrown in an actual ditch and left there to sit for weeks.
The worst state of a pony that
I ever owned would either have to be my first pony (glitter symbol fading, dirt in hair, bite marks) or my Bridal Beauty with tail rust. I'm very picky with the ponies I purchase.
EDIT: I COMPLETELY FORGOT TWO VERY SPECIAL PONIES.
The first one was the first G1 pony I ever got, Baby Shaggy, who was
coated in this brown markings. It looks like it's only dirt so I hope to fix her up once I find her again.
The second pony...oh boy.
The second pony came from this girl I knew at school. Her family weren't the...cleanliest people on the planet and I guess her mother made money by buying stuff at thrift shops and selling them on eBay. My friend once gave me this Princess Royal Blue and...oh my. First off she reeked of some kind of combination of sweat and diapers and second off she was covered in brown splotches. Along with that I believe her symbol's metalic paint was wearing off. I took the pony, not wanting to be rude, and set her on my shelf and then never touched her again. I have no idea where she is now but I'd love to fix her up if I had the chance...