Zombie Horse Spawn is a minimalistic mod which allows zombie horses to spawn with a zombie riding it. Whenever a zombie 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.
chanceSurfaceZombieHasHorse default 0.05, min 0, max 1.0 The chance a zombie that has spawned on the surface is riding a horse.
shouldBurnZombieHorsesInDaylight default true If enabled, burns zombie horses when daylight shines upon them.
onlySpawnZombieHorsesOnSurface default true If enabled, a zombie horse with rider will only spawn on the surface.
You may freely use this mod in any modpack, as long as the download remains hosted within the CurseForge or Modrinth ecosystem.
Serilum.com contains an overview and more information on all mods available. For issues, ideas, suggestions or anything else there is the Github repo. Thanks!