Mostly, the people seeking advantage of astrology remember it in the time of distress.  Therefore, the first thing is to gauge the strength of the planets so that the malefic influences on the weak planets can be analyzed.  The most malefic influence in a nativity is that of the lord of the eighth house if it contains a mooltrikona sign.  However, if it does not contain a mooltrikona sign, the title of the most malefic planet passes on to the lord of the twelfth house if there is a mooltrikona sign.

Further, if, both the eighth and the twelfth houses do not contain a mooltrikona sign, then the title of the most malefic planet passes on to Ketu.

The close impact of the planets is gauged through their closeness to the natal positions i.e. a longitudinal distance of less than 5 degrees.  Besides the natal position of the planets, there is mid-point or the most effective point of each house known by the degree rising in the ascendant.  Suppose an ascendant of 16 degrees  rises.

It means the mid-point or the most effective point of each house would be 16 degrees.  The most malefic planets in any house having a longitude between 11 to 21 degrees would malefically influence the most effective point of the house of its placement and the house(s)/ planet(s) aspected by it or the planet(s) in conjunction with it.

For the convenience of the readers, the following are the most malefic planets (MMP) for the various ascendants.

ASCENDANT    MOST MALEFIC PLANET (MMP)

Aries                           Ketu
Taurus                        Jupiter
Gemini                        Ketu
Cancer                        Saturn
Leo                             The Moon
Virgo                           Mars
Libra                            Mercury
Scorpio                        Venus
Sagittarius                    The Moon
Capricorn                      The  Sun
Aquarius                       Mercury
Pisces                          Venus

If the planet or the lord of the house, with which the most malefic planet is forming a close conjunction/aspect, is strong and well placed, this most malefic planet creates tension(s) with regard to the matters represented by the house/planet involved.  When the afflicted planet is weak, the significations suffer seriously.  When the afflicted planet is weak and badly placed, it results in tragic happenings.  To understand the difference between tension, serious trouble and tragic happenings consider the situations of fever, jaundice and the loss of a limb ruled by the concerned planet, respectively.   The transit impact of slow moving stationary malefic planets triggers the trouble.  When the affliction is close to the mid-point of the house, significations of all the houses involved, that is the house occupied and the house(s) aspected, suffer.  In the case of the afflicted planets, besides their general significations, the significations of the house (i) where the mooltrikona sign is placed, and (ii) significations of the house where the planet is placed, suffer.  The descending order for the weak planets is a combust planet, bad placement, debilitation, old age, infancy, debilitated in navamsa and the weak dispositor.  The weakness of planets is effectively strengthened by use of a KAVACH to a large extent.