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 invalid, shooter as LivingEntity, xPower as double, yPower as double, zPower as double) as SmallFireball
new SmallFireball(level, shooter, 0, 1, 2);

Parameter	Type	Description
Parameter level	Type invalid	Description The level this entity is in.
Parameter shooter	Type LivingEntity	Description The entity that created the fireball, used to get the position.
Parameter xPower	Type double	Description The x power of the entity.
Parameter yPower	Type double	Description The y power of the entity.
Parameter zPower	Type double	Description The z power of the entity.

ZenScript
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new SmallFireball(level as invalid, x as double, y as double, z as double, xPower as double, yPower as double, zPower as double) as SmallFireball
new SmallFireball(level, 0, 1, 2, 3, 3, 3);

Parameter	Type	Description
Parameter level	Type invalid	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 xPower	Type double	Description The x power of the entity.
Parameter yPower	Type double	Description The y power of the entity.
Parameter zPower	Type double	Description The z power of the entity.