As 12th house represents the things person would sense a kind of loss about, 8th house represents things which would go through some changes in life and person may not feel stable about those things because 8th house is house of changes. I am not taking the dignity of planets in consideration here, with my earlier post about 12th house and now about 8th house of changes, because the basic foundation of 12th house is of losses and basic foundation of 8th house is instability. Of course, nothing is permanent in life and things improve with age and experience. This is where I am saying that "to begin life" person will have these feelings of losses or changes, as the case may be.

So, whichever planet is in 8th house, person can experience major changes in life related with that planet. Like,

Sun - Person will feel that he always meets those people who hurt his ego and his career can see many changes and instabilities. 

Moon - It is marana-karaka position of Moon where mind feels continuous fear of upcoming changes. 

Mars - Transformative relation with brother/male friends and person may be fearful in overall approach as Mars represents courage and will-power. 

Mercury - Relation with siblings can go through instabilities. Person can have fluctuating interests or hobbies. 

Venus - Overall love life or relations can go through major changes. Person may never feel stability in relationship. 

Jupiter - Person's belief system or morals can go through a major change. 

Saturn - Major changes related with duties and responsibilities in life. Changes may not be sudden here due to slow nature of Saturn. It means person will get many opportunities to correct himself before a major change comes in life.

I would again not consider Rahu-Ketu for these concepts as they give results based on sign and sign lord position plus conjunction with them. But it doesn't mean that they don't have any impact at all in 8th or 12th houses.

Rahu in 12th house can make someone gain from foreign lands but person can have spendthrift nature. Rahu in 8th house can explode changes and bring lots of changes but person can be a perfect mystic.

Ketu in 12th house is considered as Moksha-Margi position of Ketu but it can give some very weird or split spiritual views. Ketu in 8th house can split your family property or inheritance but again it creates someone who spends immense time in research of occult matters.

Needless to say that if 8th house is empty then 8th house lord position will decide where the change is coming.

Someone asked similarities between 8th house and 12th house. Well, they both deal with secret matters. They both are part of moksha triangle along with 4th house. They both represent our intuitive abilities. 12th house is 5th from 8th house, so it represents education of occult and mysticism. 8th house is 9th from 12th house, so it represents luck of spiritual pursuits and foreign lands.

Understand a house as a Land Property you have. Sign as a Home you built. Planet as the person residing in that home. Now, if your title of land itself is doubtful then no matter how beautiful is your home or how strong is your tenant, you may find trouble in asserting your right on property. This is what happens with Dushthana houses like 6th, 8th or 12th that their base significance itself is malefic by nature. So, it will give some malefic results anyhow.

Thanks, 

SPB