Mercury in Pisces are slightly more queer. Here we wade into the murky waters of the dreamworld, where things are no longer straightforward and factual, but are meandering, multiplicitous, mysterious, evasive. Mercury in Pisces speaks in whispers and in psychic impressions, works with information that is not straightforward, thinks in symbols, searches for things that are not immediately accessible and takes interest in subjects related to the mystic, unknown, obscured, or somehow beyond the confines of regular language.
There are so many ways that this can show up. For those that are scientifically-minded, they may study things that are really challenging to understand or have no clear answers, like studying outer space, or deep oceans, or working with chemistry and biology to understand what goes on at the molecular level in the body and thereby develop medicines, therapies or technologies that address current gaps in our understanding or capacity.
Similarly, Mercury in Pisces people can find their place in fields where information is not easy and straightforward, they have to figure things out as they go. For instance, they may work with insurance policies that have ambiguous criteria, or they can be in the financial field trying to predict movements in certain asset classes in order to make their trading strategies, or they can work in meteorology attempting to foresee weather patterns and likely outcomes.
Mercury in Pisces are also very likely to take interest in some foreign language, which can literally be a language spoken in another nation, so it is common that they immigrate or they live in communities that represent many different languages and cultures, and may sometimes interact with people who do not speak their native language well. They can also take interest in sign language or animal communication, which can be just about behavioral study and body language, but can also be in the form of receiving psychic impressions or feeling very close to non-human beings, but this is not the case for everybody.
Pisces Mercury can also receive messages in their dreams and frequently contemplate the things that happen to them outside of their regular consciousness, and investigate more existential questions, such as the origin of one's existence, or the philosophy that makes sense of everything in life, or they might often meditate or listen to calming sounds that help them get in touch with a slower, more ambiguous frequency of thought that is non-linear. So they can absolutely be experimental, more open to different influences, like trying various substances, or having some kind of mental different-abilities like being mute, autistic, lyrical/musical/poetic, etc.
On a similar note, Mercury in Pisces can find themselves somehow mired in religious themes, growing up around strictly religious people, for instance, and hearing all their life about sin, about the expectations of God, about the stories from holy texts, and so forth. They themselves can become very religious in their adult life, or otherwise have some sort of strong spiritual practice that takes them outside the strictly logical world and into more ambiguity and faith. So if they are not Christian or Muslim or Buddhist or whatever else, they can instead practice yoga, or follow the teaching of Law of Attraction, or study the I-Ching, or of course take great interest in Astrology, or read the writings of various Gurus – they like to see beyond the veil.
They're also likely to be very much into some fantasy worlds. For some, this can be a love for film, maybe an affinity for a particular science fiction world. Or perhaps they love to read and get lost in various stories that obviously do not exist in reality. And they can be very much into mysteries like Sherlock Holmes or various TV shows that are in that category. Mercury in Pisces essentially investigates the widely unknown, or unclear.
It's very common for them to be in someway artistically gifted, be it through music or painting or poetry, where they can bring out different feelings both in themselves and in other people, but for them the world of FEELING is of tremendous import. Their strong skill is intuition, sensing, less so than knowing and referencing tangible facts. Mercury in Pisces does perceive the world at least in part through the imagination, and can develop very complex worlds in their mind that are difficult to communicate to other people. Music especially comes to mind given that they are reading notes and translating them into sounds on an instrument, and they can play multiple instruments also. And similarly, in their art they may focus on symbolism throughout.
Of course, given that Pisces is a water sign, Mercury here is also likely to work with the water quite some. They may get their best ideas in the shower, they may love to go for a dip in the ocean, they might be particularly clean and tidy (though some can deal with the opposite due to Pisces' chaotic nature – have loads of chaos either in interpersonal communication or physical chaos through absence of cleanliness, which can sometimes come as a result of people they live with rather than their own messiness), or they can be extra sensitive about hygiene of any sort. They're likely to spend lots of time in the bathroom, cover themselves in various scents or creams, and make sure that the atmosphere in their house is made more cozy by the use of incense or candles or little trinkets here and there.
They might take fascination with the ocean or with bodies of water at large, feel a mystic connection to the water and literally work with the water in some form. For instance, they could work with fish, or study the natures of lakes and rivers, or work in public sanitation, or as chemists in laboratories, or on the water as sailors… the list is endless. They can equally take interest in outer space, by the way, given its distance and vastness, which perfectly fits the nature of Pisces. Lastly, their communication with other people can sometimes be more unclear. They can keep secrets or tell lies or try and communicate a story but end up going on different tangents and not getting to the point. And they can sometimes be cryptic or speak in parables, like how poets do, relaying information indirectly through metaphor or by sounds, etc.
And they're likely to be somehow calmed by ocean sounds, by the noises that marine life makes, or by running water, so they could certainly live near bodies of water where they constantly hear it bubbling, streaming, swishing or crashing onshore.