Requires the library mod Collective.

This mod is part of The Vanilla Experience.
Giant Spawn is a minimalistic configurable mod which allows giants to spawn naturally. Whenever a zombie spawns it has a chance to be a giant, by default 1/20 and only on the surface. The mod also adds a custom AI to the giants based on the zombie AI.

You may also be interested in Skeleton Horse Spawn or Zombie Horse Spawn.

Configurable
chanceSurfaceZombieIsGiant (default = 0.05, 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.

giantMovementSpeedModifier (default = 1.0, min 0, max 20.0): The giant movement speed modifier relative to the base zombie movement speed.
giantAttackDamageModifier (default = 2.0, min 0, max 20.0): The giant attack damage modifier relative to the base zombie attack damage.

The giant moving with its custom AI:

giantmoving