Natal Pluto is the sign where your Pluto was placed during birth time, and from there other houses are calculated clock-wise.
If you were born with Pluto in Sagittarius, then your natal house is Sagittarius (Dhanus Rasi) and during transit, MERCURY forming conjunction (in Sagittarius), sextile (aspect of 60° which are Libra and Aquarius in this case), square (aspect of 90° which are Pisces and Virgo here), trine (aspect of 120° which are Aries and Leo here), opposition (aspect of 180° which is Gemini here) are discussed in this article.
Conjunction is transiting through same sign as in birth chart, sextile is transiting 3rd or 11th house, trine is transiting 5th or 9th house, opposition is transiting 7th house from natal sign.
Transit Mercury conjunct Natal Pluto : Uncompromising attitudes, irrevocable decisions, mental domination characterize this transit. The native is very inquisitive to reach the root of every question, thus fit for research and investigation work. The native speaks in a persuasive and forceful manner that others are convinced. The native is good analyst of human nature and is interested in the study of advanced scientific subjects and parapsychology. Under stress aspects to conjunction the individual either experiences or subjects others to mental domination and coercion.
Transit Mercury Sextile Natal Pluto : Understanding of cause and effect phenomenon characterize this transit. A good time to study subjects of deeper knowledge such as psychology, astrology, physics, mathematics, economics, genetics and sex and to get to the root of the truth. This is an investigators transit and it is very difficult to conceal anything from the native. The individual has the ability to change people’s thinking. Trade union leaders have this transit in their natal charts. A time to take decisions regarding joint finances, taxes, insurances and inheritances. There may be short trips related to business and financial activities.
Transit Mercury Square Natal Pluto : Mental coercion, power struggle, conflicts, secret investigations characterize this transit. The native has difficulty in taking business decisions and feels uneasy while keeping a secret information. Not a good time to sign any agreements. The native is forced to discard old concepts radically for large scale problems affecting the humanity and civilization as a whole. The native has problems due to unpleasant or disturbing psychic or telepathic experiences.
Transit Mercury Trine Natal Pluto : Enhanced scientific and occult insights and clear clairvoyant perceptions characterize this transit. The native is intellectually interested in science, sex, parapsychology, economics and pursuits requiring exploration. The native tends to learn new things and subjects. A better time for business or professional planning and for signing contracts. The native is conscious about his health, diet and personal hygiene. The native is able to impress people by his lecturing ability and communicating skill.
Transit Mercury opposite Natal Pluto : Mental coercion, fanatic planning, suspicion and sarcastic speech characterize this transit. The native is engaged in secret investigation for finding the truth. The native should be careful in making an opinion about others and himself also. Circumstances may force drastic changes and present new situations to live with. Suspicion in one’s mind may result in spying intrigues and secret communications. Occupational hazards, environmental pollution or ecological imbalances endanger the health.
The individual may be subjected to problems related with evacuation and psychic disturbances. The native may be interested in life after death mysteries, reincarnation and such occult studies. The native is required to beware of deep thinking while driving.