Further Evidence that Aaravos was Imprisoned with Moon Magic
So we know the effects of ghosting through Rayla. It silences and "vanishes" the accused from the eyes of the community. Said community could only see the banished, however, in reflections, but could not hear them. Ethari and Rayla as an example:
If one sees Aaravos in the mirror, technically, no one is able to hear him speak. Unless a pact had been bound with a person and Aaravos’ worm, but let’s assume they have not. I think the "ghosting" effect had similarly been done to Aaravos, because the reason why Viren (and anyone looking into the mirror) is able to see him, is because we are seeing his reflection in the mirror. Viren is only able to hear Aaravos because of the pact he had with him, like how Ethari casted a temporary spell in order to see and hear Rayla again.