Looks like a mini with some kind of dwafism. My aunt breeds minis and a couple people that she knows inbreeds them too closely and they get a dwarf-ish mini every few years... My Aunt has NEVER gotten a dwarf or otherwise deformed mini, and her herd has been closed for 20 years now (no new outside blood). She's careful about who gets to breed and she sells the young ones that are too closely related.
Easy stomach, Easy Stomach, That thing should of had a warning on this thread about the photo. I can't image why anyone who bred a shetland pony to a New Forest pony. That thing is ugly and I bet it will have problem later in life.