Having Mars transiting your 8th or 12th natal house is not an easy period of time. the 8th and 12th are internal, intimate houses. Having Mars there is like having an elephant in a china store – mars shows its malefic side when entering any of these houses since naturally he is an energetic, external and aggressive planet, while these houses are delicate, receptive and passive.
Usually having Mars in either the 8th or 12th natal house indicates a sensitive time in which some deep fears, resentments, phobias, anxieties and intrigues arise.
The 8th house, being more partnership related, may arise fears and harsh feeling towards other significant people. Issues of trust are likely to harm the image of the other person and to interfere with otherwise smooth relationships. Self doubt is less likely here: the 8th house is about inner drive so with Mars here there might be a feeling of having no energy anymore. feeling drained or exhausted from life is likely with this transit.
The 12th house is more related to general phobias, depression and fears. A person with Mars transiting this house may feel overwhelmed by the world, may have problems communicating their feelings and sharing their fears therefore the result might be feeling isolated and alone. Sleeping problems and addictions may also be a cause for a more lasting depression when transiting Mars is in the natal 12th house.
These two houses are also connected to self strength so having Mars in any of them may result in feeling weak, helpless and hopeless. Mars in these houses tend to take energy instead of giving energy so the usual self strength, emotional ease, confidence in life that a person feels may turn into less favorable feelings.
Since mars transits a natal house for at least 2-3 month, the manifestation of its influence on the 8th or 12th house won’t be short and sharp. Instead, a sensation of isolation or mistrust will start build themselves from the moment Mars touches the cusp of the house. later on there will be a period of building up all the negative emotions, dealing with them and learning how to handle them, to a point that usually when Mars left the house, the person feels a huge relief, but not sudden and surprising one – rather a feeling that they themselves learned how to rule their fears.