In a Vedic Astrology Kundali (Chart) there are 12 houses each representing 12 different sectors of life.
1st house- Personality, Physical Appearance
2nd House- Wealth, Family
3rd House- Siblings, courage
4th House- Mother and Home
5th House- Children and Speculation
6th House- Debts and Diseases
7th House- Marriage and Spouse
8th House- Death and Inheritances
9th House- Fate and Spirituality
10th House- Fame and Public Reputaion
11th House- Dreams and Income
12th House- Expenses and Losses
There are many more areas that each house represents but for this article these broad areas are sufficient.
Whenever a planets Moolatrikon sign rules the 6th, 8th, or 12th House in the astrology chart then that planet acts as a Functional Malific.
Moolatrikon- The planets primary rulership.
Moolatrikon Signs for each planet are- Leo for Sun, Cancer for Moon, Aries for Mars, Virgo for Mercury, Sagittarius for Jupiter, Libra for Venus, and Aquarius for Saturn.
Rahu and Ketu are considered as demons in Vedic Astrology and hence they are malific for all Ascendents.
The Malifics for each ascendent:
Aries Ascendent- Mercury because he rules the 6th house of debts and diseases. No moolatrikon sign is placed in the 8th and 12th house.
Taurus Ascendent- Mars because he rules the 12th house of expenditure and losses, Venus because he rules the 6th house of debts and diseases and Jupiter because he rules the 8th house of Death.
Gemini Ascendent- No malific planets except Rahu and Ketu. No moolatrikon sign is placed in the 6th, 8th or 12th house.
Cancer Ascendent- Jupiter because he is lord of 6th house of disease and Saturn because he is lord of the 8th house of death. No moolatrikon sign in the 12th house.
Leo Ascendent- Moon because he rules the 12th house of expenditure. No moolatrikon sign in the 6th and 8th house.
Virgo Ascendent- Sun becuase he rules the 12th house of expenses, Saturn becuase he is lord of the 6th house of debts, and Mars because he is lord of the 8th house of death.
Libra Ascendent- Mercury becomes lord of the 12th house of losses and expenses. No moolatrikon sign is there in the 6th or 8th house.
Scorpio Ascendent- Mars because he becomes lord of the 6th house of disease and Venus because he is lord of the 12th house of expenditure.
Sagittarius Ascendent- Moon becomes lord of the 8th house of death and is tremendously malific.
Capricorn Ascendent- Jupiter becomes lord of the 12th house of losses and Sun lords over the 8th house of death and hence they become prime malifics.
Aquarius Ascendent- Moon is malific because he rules the 6th house of disease and the Mercury because he rules the 8th house of death.
Pisces Ascendent- Saturn becomes malific because he rules the 12th house of losses, Sun because he rules the 6th house of debts, and Venus because he rules the 8th house of death.
Secondary Rulerships-Mars rules Scorpio, Mercury rules Gemini, Jupiter rules Pisces, Venus rules Taurus, and Saturn rules Capricorn.
This is the reason why Mars acts a malific for Scorpio Ascendent even though he rules Scorpio. Scorpio is placed on the 1st house but cannot supersede Mars' Aries rulership of the 6th house of disease.
Similarly for Taurus Ascendent Venus acts as a malific. Taurus on the 1st house cannot supersede Venus' Libra rulership in the 6th houses.
Whenever these functional malifics for each ascendent aspect a planet natally or by transit they cause lots of trouble to the planet.
Example: For Sagittarius Ascendent Moon is the main malific. Wherever he goes he will create death like situations because of his rulership of the 8th house. If he conjuncts Jupiter for example he can cause physical damage due to accident. Jupiter is the Lord of the ascendent which rules the physical body and accidents are ruled by the 8th house.