I don’t know the most dangerous horoscope. But the horoscope of the most dangerous person will be the most dangerous horoscope. Now, I think here dangerous means, the one who is evil or having low level of ethics and a bad soul.
Now, I can give a hint to identify such a bad thing in a horoscope.
Sun is the significator of the soul, and Leo is his sign. So, focus on them. Whether they are in good influence or bad. Bad means affected by gulika, mandi, rahu, Saturn, parivesha.
Now, Atmakaraka is the chara significator of the soul. This should be bad, means having above mentioned affection and Gnatikaraka also. Using Jaimini aspect.
2nd house is the sanskara or can say ethics. 5th house is the storage of it. So, similarly analyze them.
Last is moon, the mind. It should be evil for sins, and so is karma karaka, i.e. 10th house/lord. So, is mercury.
Above points should be seen in D-1, D-9, D-24 and the D-45. D-45 is the most important.
Note: Above points should be analyzed sharply. Result will only fell if all these points are satisfied, with no saving factors.