SC2Mapster

You will notice the models have a bone called Attacher, this is required for them to function as a tentacle/beam. With the spine crawler you will notice that the weapon attachment point which has the attacher bone is given the name tentacle attack on the Unit actor. Under the events of that actor you will find several triggered on the signal TentacleRetracted. The reference clear event action resets the reference back to default.

The other part of the puzzle is the Missile actor used by the ammo unit of the Launch Missile effect of the attack. Under the events you find it uses a reference set event action to set the host subject of the attachment to itself and on destruction sends the signal that it is known as tentacle retracted.

The Reference Set event action works as follows. You find it has 3 fields, the Target is what the reference set is applied to (can be another actor), the Reference Name is the group of fields to modify (usually a system reference or a custom made reference) and the Reference Source which is what value to put into the associated Reference Name field.

For example if the target was set to ::Supporter and the Reference Name field was set to ::Host you can change where the supporting actor subject is hosted on (Hosting - Host - Subject) via the Reference Source field where ::Self would be the actor sending the message.

Sadly it is merely an accumulation of a few very talented contributors and even fewer doing R&D.

That is more a repetition of how the spine crawler works but used as an attachment. That tutorial was made during the beta where the leviathan was not available as an example, it even got the wrong SOp for turning the actors. Although he did update it a little