Determination of Malefic and Benefic Planets

To determine malefic/benefic planets from the ascendant, the following factors are also considered.

Lord in the Sixth, Eighth, and Twelfth House.

If the lords sit in the sixth, eighth and twelfth house, then they decrease the malefic/benefic effect of the house. Likewise, if any planet sits in these houses then it faces depreciation in benefic results. The planets which are in conjunction with the lords of the sixth, eighth and twelfth house provide inauspicious results.

Lord of any of the Houses among 3, 6, 11  and the Lord of 8th House.

The third, sixth and eleventh house is called the Trishadhaya Bhava. The lords of these houses give bad results. If any sign of a planet sits in any of the above said houses i.e third, sixth and eleventh house, and any second sign in eighth house then the planet gives bad results for an ascendant. For example :

Ascendant

Planet

The Lord of the House

Scorpio Mars The lord of eighth and third house is not auspicious for Scorpio ascendant. But Mars is able to maintain its auspiciousness, because of the Lagnesh.
Taurus Mercury Mercury is malefic because the lords of eighth and eleventh house sit here.
Pisces Venus It gets malefic because of the lords of eighth and third house.