Mercury conjunct Neptune is the most potent combination for poetic and magical thinking. It supplies the native with a gushing well of imagination that knows no bounds. At its most positive, this aspect is fabulous for the artist or musician because it works so well with non-verbal communication.
Neptune is associated with right-brain, non-rational thinking and with Mercury you might imagine that this aspect could cause learning difficulties and foggy recall. This can be true if negatively aspected, but generally, the conjunction seems to be very gifted in glamourising information and showing things in their best possible light. The Instagram filter is your best Mercury/Neptune tool as is the advertiser’s dream application, photoshop.
“ The typical Mercury/Neptune person has a gift for distorting reality. A distortion can be highly creative or dangerously misleading, It’s a common combination for those who work in the media and more especially the advertising industry” 
Mercury conjunct Neptune can be very psychic and it is also able to infiltrate the minds of others. Most often this is done by brain-washing with subliminal imagery and romantic, tear-jerking music. You see this done so well within the movie industry and in pop promo videos. It is interesting so many industry songbirds are on the list below, plus a couple of porno stars too. I guess that would show Neptune’s dissolving of boundaries pretty blatantly.
Of course, lying would be one of Mercury conjunct Neptune’s worse manifestations and this also leads to making one a skilled propagandist. This is not then really the position of the scientist or the engineer as this aspect can so readily make adjustments to the truth. However, social engineering in the form of the Tavistock institute kind would resonate strongly with this archetype.
Mercury conjunct Neptune is a gift to the psychologist as they will be able to read their patient very well. On the other hand, this can also be the narcissist that carefully studies the psyche of their prey so that they can manipulate them. Of course, ‘gas-lighting’ would also be possible too with this aspect.
Mercury Conjunct Neptune ~ Natives
Rudolf Steiner was born with Mercury conjunct Neptune. He was famous for trying to find a bridge between science and spirituality. Steiner was a philosopher, social reformer, architect and esotericist. Steiner’s early spiritual experiences demonstrate his Mercury conjunct Neptune really well. At aged Nine he saw the spirit of his aunt asking for help just before she committed suicide before any of his family knew.However, Steiner kept his psychic abilities under wraps and during his early career, he is generally seen as the Mercurial scholar. That is until he ‘went mad’ (or Neptunian) after the age of 40.
“Steiner first began speaking publicly about spiritual experiences and phenomena in his 1899 lectures to the Theosophical Society. By 1901 he had begun to write about spiritual topics, initially in the form of discussions of historical figures such as the mystics of the Middle Ages.” ~ Wikipedia
Not surprisingly for a Neptunian thinker. Steiner had at one time close ties with the Theosophical society, but viewed it through a more western lens. Wikipedia continues;“In 1899 Steiner experienced what he described as a life-transforming inner encounter with the being of Christ; previously he had little or no relation to Christianity in any form. Then and thereafter, his relationship to Christianity remained entirely founded upon personal experience, and thus both non-denominational and strikingly different from conventional religious forms….”
Wikipedia goes on to state; “Steiner’s views of Christianity diverge from conventional Christian thought in key places and include gnostic elements… However, unlike many gnostics, Steiner affirms the unique and actual physical Incarnation of Christ in Jesus at the beginning of the Christian era.” Rudolf Steiner’s life is a great example of the themes of Mercury conjunct Neptune. His conjunction, perhaps not surprisingly, was in Pisces!