This mod is part of The Vanilla Experience.
A minimalistic configurable mod which allows giants to spawn naturally. Whenever a zombie spawns it has a chance to be a giant, by default 1/40.
You may also be interested in Skeleton Horse Spawn or Zombie Horse Spawn.
chanceSurfaceZombieIsGiant (default = 0.025, min 0, max 1.0): The chance a zombie that has spawned on the surface is a giant.
shouldBurnGiantsInDaylight (default = true): If enabled, burns giants when daylight shines upon them.
onlySpawnGiantOnSurface (default = true): If enabled, a giant will only spawn on the surface.