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.
Mrigshira - Mrigshira is nakshatra of desire oriented people. Someone who is keep searching for his next desire satisfaction. It is a nakshatra of disguise too. It is also related with Spying or Stalking and travelling. Please read this to get detailed info about Mrigshira - https://www.astrosaxena.com/mrig.
Taurus - As Mrigshira is part of Taurus, Taurus sign and its representations become important here. Taurus is the 2nd sign of zodiac belt, so it represents many things related with 2nd house of horoscope like, Hoarded Wealth, Assets, Savings, Finances, Luxuries and Liquid Money. All in all a sign related with luxuries and all the conveniences of life. Taurus is consisted of 2 and half Nakshatras, i.e. Krittika, Rohini and Mrigshira. Taurus' lord is Venus.
Gemini - As Mrigshira is also a part of Gemini, Gemini sign and its representations become important here. Gemini is the 3rd sign of zodiac belt, so it represents many things related with 3rd house of horoscope like, Communication Skills (either written, oral or even by sign language), Marketing, Business etc. It is a sign basically related with communications and business ideas. Gemini is divided into 2 and half nakshatra of Mrigashira, Ardra and Punarvasu. Gemini's lord is Mercury, which is significator of Communications.
Venus – As Venus rules Taurus, Venus’ position and dignity is important to know about the overall functioning of any planet in Mrigshira/Taurus.
Mercury - As Mercury rules Gemini, Mercury’s position and dignity is important to know about the overall functioning of any planet in Mrigshira/Gemini.
Mars - As Mrigshira is ruled by Mars, Mars's position and dignity will also have an important role in functioning and results of any planet in Mrigshira.
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 Mrigshira Nakshatra – When Mercury is in Mrigshira Nakshatra, it is in enemy nakshatra as its lord Mars and Mercury are mutual great enemies. At the same time, Mercury remains in friendly sign in Taurus ruled by its best friend Venus and in own sign Gemini. Mercury and Mrigshira both are related to travelling, curious nature and research. So, these people can be very research oriented and curious to know new things. They can also be working in some research oriented field. Even in personal life, they can be interested in spying or stalking at people. They can also be in travelling related business. Due to sexual nature of Mrigshira story and flirtatious nature of Mercury, they can be very sexual by nature and may not limit themselves to only one partner. They can be desire-blinded and can seek satisfaction to their never-ending desires. In Taurus section, they can be very good with financial matters and can gain wealth out of the above activities. In Gemini section, they can be in business related with these matters and would love to communicate about these matters. They can be highly communicative or extrovert in Gemini section. Overall, this planetary position shows that person needs to learn that none else can make anyone happy. Our happiness, we need to seek within ourselves. Until and unless they learn that, they may continue to pursue their endless desires blindly.
Role of Venus – Venus's position will become important in functioning and results of Mercury in Mrigshira/Taurus as Venus rules Taurus. If Venus is in good dignity then Moon will have proper direction.
Role of Mercury – As we are trying to interpret Mercury only, we need not to see Mercury's position separately.
Role of Mars - Mars's position will also become important in functioning and results of Mercury in Mrigshira as Mars rules Mrigshira. If Mars is in good dignity then Mercury will have proper direction.
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 Mrigshira. 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 Mrigshira can work in a chart.