8, 6 and 4 in relation to an ascendant, it is quite scary.
It should be scary in the case of Rahu (8) is powerful.
That is as Maha Chakra or exaltation or pre/post-exaltation and related to an ascendant. Since Rahu (8) means addiction, tricking, gambling, deception, etc.
Therefore, a person with strong Rahu (8), if he is addicted to something, it will be very serious. He is cunning or deceiving others. He might be heavily addicted to alcohol, drugs or gambling (see other planets also).
Venus (6) means the artistic issues, imagination and fancy. Combining both strong Rahu (8) and Venus (6) (with good dignity and related to an ascendant) would have a property of acting (art + deception), but it has tendency to be a tricking.
For a Mercury (4) is an information, deliberation, conversation, therefore, a person who has all 3 planets like this related to an ascendant would be well-spoken, rhetorical, artistic in a way of tricking, straight-faced in lying.
Also, the relation to his ascendant means it is congenial to him too. Entirely, whether it is lying, tricking, it will be congenial. There is very little chance of being caught.
If a Jupiter (5) is not related to an ascendant, he will lack of good judgment. It will result as a person of “deceiving people until death”.
I met this kind of people myself. It is really scary.
Notes: – If Rahu (8) is normal or impaired, it will not result as this case. Rahu (8) as a domicile, is not quite scary because he will be good at deceiving when he is old (but he is untrustworthy anyway.)
The seriousness depends on the planets’ dignity and their relation to an ascendant with further details. Its main principle is only this.
A neutral Rahu is still vicious
Case Study 01021