Oh, for that, for enemies/bosses, see entity.initial_movement_driving_bullet_pattern
If you want the movement-driving-pattern to start at some point other than initial spawning of the entity, see EffectType.StartMovementDrivingPattern (to time delay that, give it OnUse timing and put it on a system on the entity, with that system having one unit of ammo and either cue_time or initial_firing_delay set to the desired time)