A thing to remember here is that these posts are strictly meant for the particular planet position. Like, today we are looking at Mercury in Pisces, so the description given here may change for you if your Mercury is although in the sign of Pisces but with conjunction with or aspected by other planets.
So, lets see what Mercury can do in Pisces without any conjunction or aspect from any other planet. 1st lets see what these 2 things represent --
Mercury represents communication skills, marketing, calculative ability, younger siblings, hobbies, skills with hands, intelligence, quick decision making, logical thinking, youthfulness etc.
As Pisces is the 12th sign of zodiac belt, it represents the same energy and things which are represented by 12th house such as Isolated Places, Spirituality, Imagination, Other Dimension or Other World etc. Besides these things, it also represents your Hidden Talents, Ability to work in background, Spiritual Self etc. Pisces is consisted of last 2 and half nakshatra, i.e. Purva-Bhadrapada, Uttara-Bhadrapada & Revati. Pisces' lord is Jupiter.
So when Mercury is in Pisces, it gets debilitated at 15 degrees. Why? Mercury is intellect of a person and Pisces is sign of imagination and dreams. So, intellect of person is severely effected as person remains in dream world or imagination. Most of the decisions taken by such person are based on mere imagination. Hence, Mercury is debilitated.
But Mercury debilitation is one for which I least care. Of course, it can give some issues related with siblings or skin related health issues but it is a beneficial position when it comes to writing. As person's communications are all about imagination, they can have great imagination abilities and later they can write about all these imaginative thoughts. This only means that Mercury debilitated can actually create the best of authors. They can write the best of stories and novels and get all kinds of awards for such actions. But in personal life, this Mercury retrograde can still create trouble as people may not be able to understand as to what person wants to say.
As always, Mercury's placement in different nakshatra will change this scenario as per the position of Nakshatra Lord. If Mercury is in Purva-Bhadrapada Nakshatra, its lord Jupiter's position would impact Mercury. If Mercury is in Uttara-Bhadrapada Nakshatra, its lord Saturn's position would impact Mercury. Likewise, if Mercury is in last nakshatra Revati, then it is best for Mercury as it is in its own nakshatra.
Overall, Mercury will be impacted most by the condition and position of Jupiter in Horoscope as Jupiter is lord of Pisces.
Vishal S Saxena - Astrologer