The Calyrex rider forms seems to fix a lot of the Horses problems, which is great.
Ice Rider gets Leech Seed, Life Dew, and Trick Room, to provide it with longevity as well as to take advantage of its low speed
Shadow Rider gets Psychic/Psyshock, Giga Drain, Draining Kiss, Tri Attack, Leaf Storm and Pollen Puff to increase its shallow movepool
Curious to see how the Ice riding form fares, since it's got a bad type combo and is still very slow. But its stat total is still pretty bonkers for a place like OU.