Let’s look at important things here –
Mercury - Mercury represents communication skills, marketing, calculative ability, younger siblings, hobbies, skills with hands, intelligence, quick decision making, logical thinking, youthfulness etc.
Uttara Bhadrapada Nakshatra - It is a nakshatra related with next stage of Purva Bhadrapada. Hence, it is nakshatra of the actual event of liberation or enlightenment. It also represents all type of mystical subjects, practices and experiments. Please check this link for more info on Uttara Bhadrapada Nakshatra - https://www.astrosaxena.com/ubnaksha.
Pisces - As Uttara Bhadrapada is a part of Pisces sign, Pisces and things represented by Pisces are also important here. 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.
Saturn - As Saturn rules Uttara Bhadrapada Nakshatra, its position and dignity is important to know about the overall functioning of any planet in Uttara Bhadrapada.
Jupiter - As Jupiter rules Pisces, its position and dignity is important to know about the overall functioning of any planet in Pisces.
Houses Involved – Also, we can’t afford to forget the houses involved as a planet can be ruling different houses and sitting in different house for every person as per ascendant and planet’s position. To know overall affect, we have to consider the houses involved as those areas of life are being impacted.
Interpretation of Mercury in Uttara Bhadrapada Nakshatra – Now, Mercury is in friendly nakshatra and enemy sign where it also goes debilitated. At the same time, Mercury debilitation is one thing which I am not much concerned about. Mercury in Pisces can make person very creative, imaginative and spiritual. They are normally seen as good writers. Although, Mercury debilitation is something which can bring relationship issues if Mercury is a relationship oriented planet and it can bring health issues related with Mercury but in creative nature of work, Mercury in Pisces is very good position.
Uttara Bhadrapada Nakshatra is closely connected with higher level of spiritual and mystical experience. As Mercury represents business and communication, it shows someone who is in business, communication or counselling related with spiritual, mystical or occult related matters. They can be interested in collection of information related with these matters. They can easily work as spiritual or mystical counselor or preacher. At the same time, it can create a spiritual Guru who can be a fraud too as there is lot of mysticism involved with this nakshatra. So, we may not come to know if a Guru is genuine or fraud.
As Mercury is debilitated, if it is relationship oriented planet, person can be very dreamy or imaginative in matters of relationship and they may lack practicality in their relationship matters. Overall, a great position for spiritual or mystical pursuits.
Role of Saturn - Also, Saturn's placement is important to guide Mercury in right direction, being Uttara Bhadrapada lord.
Role of Jupiter - Likewise, Jupiter placement is important to guide Mercury in right direction, being Pisces lord.
Other Factors – And of course, we need to consider conjunction, aspects, house lordship, house position and dashas etc to know the exact results of Mercury in Uttara Bhadrapada. So, we always need to take a holistic view of chart rather than just 1 planetary position.
Conclusion – So, this is how I see Mercury in Uttara Bhadrapada can work in a chart.
Hope this helps. Please post any comment or query you may have.