Requires the library mod Collective.
This mod is part of The Vanilla Experience.
Skeleton Horse Spawn is a minimalistic configurable mod which allows skeleton horses to spawn naturally with a skeleton riding it. Whenever a skeleton spawns, it has a chance to be spawned as a rider. You can configure it to only spawn on the surface and if it should burn in daylight.
You may also be interested in Giant Spawn or Zombie Horse Spawn.
Configurable: ( how do I configure? )
chanceSurfaceSkeletonHasHorse (default = 0.05, min 0, max 1.0): The chance a skeleton that has spawned on the surface is riding a horse.
shouldBurnSkeletonHorsesInDaylight (default = true): If enabled, burns skeleton horses when daylight shines upon them.
onlySpawnSkeletonHorsesOnSurface (default = true): If enabled, a skeleton horse with rider will only spawn on the surface.