Ooh, spooky! This model was the Halloween Horse back in 2016. He's item #1763 on the Ruffian mold sculpted by Sue Sifton, and was a run of 3,000.
This guy had a little bit of a mixed reception, if I remember right. I guess the design is rather polarizing - a horse with a demonic skeleton "riding" it? Wild stuff. I think it's rather clever, and I like the contrast of the white areas against the black - especially the head and tail. Skull horse! Hah. I do wish he had four white socks, though - I realize he's supposed to be a "pinto" of sorts, so he wouldn't necessarily have four socks, but the completionist in me wants to see all four of them be white.
As for Ruffian herself, she's still pretty popular 13 years after her release - at least, going by the number of Breyerfest auction models she's had. 9 of them in 13 years? Sheesh. Anyone trying to collect all those will have to have some pretty deep pockets, and that's not even including all the raffle and prize models we've seen on her.
Anyway, I'm not sure where we'll see Ruffian next - she was the inexplicably unpopular special run "Dead Heat" at Breyerfest last year, as well as an auction model this year. She was a Breyerfest prize model in 2014. However, she hasn't been a web special since 2015 - maybe she'll pop up there? Or as this year's brick-and-mortar special run? I hope so - it'll be hard for me to get my hands on one! I'll just have to hope for a new regular run.