Shani mangal yoga anywhere in the horoscope has a very powerful impact mostly negative as these two planets are malefics. Shubh graha give shubh phala and paap graha will always give paap phala. Shani mangal yoga be it conjunction, opposition or Shani behind mangal and vice-versa has to be checked with proper care before interpreting results of it.
In this article I am going to talk about position of Shani behind mars or Mars behind saturn when this is called dwi-dwadarshak or 2/12 connection between both which is also not good. This yoga works like shani-mangal yuti.
When Shani is behind Mars or vice-versa the two houses involved will have their significations spoiled and have negative results for the jataka. These planets even if in 2/12 will work like being in yuti or conjunction.
I have many more cases with shani-mangal behind each other and problems related to the houses they are posited in. Whenever you have such positions be rest assured that they will work like being conjoined if any one of them or both are retrograde still worse the results. This yoga is not like actual conjunction or opposition still gives powerful results.
I will also post cases with shani mangal yuti and opposition when time permits. One thing my guru taught is Malefic planets will always give malefic results and benefic planets will always do shubh to the house they are posited in. By this rule, shani mangal yoga will always give ashubh result no matter what. It is just that it has to be analyzed properly before reaching any conclusion because aspect of a benefic planet on these planets can alter the results.