How to get, grow and ride a Happy Ghast in Minecraft
Feed it Snowballs to speed this up.

The Snowball is a throwable ball of snow, collected by digging snow with a shovel. It does no damage to most mobs but knocks them back, hurts blazes, and four of them pack into a snow block.
It cannot be crafted; it can be found in chests.
A thrown snowball pushes back the mob or player it hits, which is enough to knock someone off a ledge. Against a Blaze it deals 3 damage, so a stack of snowballs is a cheap weapon in a Nether fortress. Snowballs stack only to sixteen.
Breaking snow layers or a snow block with a shovel gives snowballs, and four snowballs craft a Snow Block back. Snow Golems throw snowballs at hostile mobs and drop a pile of them when they die, so a golem in a cold biome is a small snowball farm.
A snowball is also a treat for a Happy Ghast, which you can heal by feeding it snowballs. Dispensers in trial chambers sometimes fire snowballs at intruders.
This item has no crafting recipe.
Feed it Snowballs to speed this up.
They take no damage from fire, lava or falls, but a Snowball deals 3 damage and water hurts them.
It can be found as loot in Ancient City, Trial Chambers and Village. It is dropped by Snow Golem.
It is thrown to knock back mobs and hurt blazes, crafts snow blocks and feeds the happy ghast. It is an ingredient in one recipe: Snow Block. Animals that eat it: Happy Ghast.
Yes, up to 16 per slot (most items stack to 64).