It might be required for you to import the package if you encounter any issues (like casting an Array), so better be safe than sorry and add the import at the very top of the file.

ZenScript
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import crafttweaker.api.entity.type.projectile.SmallFireball;

SmallFireball extends Fireball. That means all methods available in Fireball are also available in SmallFireball

ZenScript
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new SmallFireball(level as Level, shooter as LivingEntity, direction as Vec3) as SmallFireball
new SmallFireball(level, shooter, new Vec3(1, 2, 3));

Parameter	Type	Description
Parameter level	Type Level	Description The level this entity is in.
Parameter shooter	Type LivingEntity	Description The entity that created the fireball, used to get the position.
Parameter direction	Type Vec3	Description The direction that the skull is moving in

ZenScript
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new SmallFireball(level as Level, x as double, y as double, z as double, direction as Vec3) as SmallFireball
new SmallFireball(level, 0, 1, 2, new Vec3(1, 2, 3));

Parameter	Type	Description
Parameter level	Type Level	Description The level this entity is in.
Parameter x	Type double	Description The x position of the entity.
Parameter y	Type double	Description The y position of the entity.
Parameter z	Type double	Description The z position of the entity.
Parameter direction	Type Vec3	Description The direction that the skull is moving in