Okay, yes, tapirs would be a fantastic and relatively unique addition. I would also not mind some giraffes, moose, gazelles, and ibexes. And how could we set aside the pigs~? Also, although they don't have "hooves", hippos and rhinos are technically classified under ungulatae...though, so are whales and dolphins... :/
Yeah, the kelpie is basically a wicked shapeshifter that just looks like a horse when it's above water, hunting (usually small children who don't eat their veggies), but they're definitely one of my favorite "evil" equine creatures in folklore. I also had the notion of one using water magic the way Velvet has her ice, and the character would have to have some serious tweaking to how its moves worked in order to keep it from being a clone, but I'd still love to see it nonetheless.