/summon Slime ~ ~1 ~ {Size:1,Invulnerable:1,Riding:{id:EntityHorse,Invulnerable:1,Tame:1,Saddle:1,Attributes:[{Name:generic.movementSpeed,Base:1},{Name:horse.jumpStrength,Base:2.0}],ActiveEffects:[{Id:14,Duration:1000000}]}}