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.
import crafttweaker.entity.IEntityArrow;

IEntityArrow implement the following interfaces and are able to call all of their methods/getters/setters as well:

• IEntity
• IProjectile

ZenGetter	ZenSetter	Type
ZenGetter shooter	ZenSetter shooter	Type IEntity
ZenGetter damage	ZenSetter damage	Type double
ZenGetter knockbackStrength	ZenSetter knockbackStrength	Type int
ZenGetter isCritical	ZenSetter isCritical	Type boolean
ZenGetter pickupStatus	ZenSetter pickupStatus	Type String
ZenGetter shake	ZenSetter ​	Type int

• void shoot(IEntity shooter, float pitch, float yaw, float roll, float velocity, float inaccuracy)

• void setPickupDisallowed()

• void setPickupAllowed()

• void setPickupCreative()