Marius. Ive watched him work. Very powerful.
In a situation like this, sometimes there is no proper "technique" but there are ways to win. First I would attack his mobility. Primarily his knees.He has to hold up a lot of weight. And if he is faster than me then I must secure a chance to escape. But it isnt limited to just his knees. Im going to attack every joint that I have an opportunity to. I want structural damage and I want to take away his will to fight.
Secondly I watch my enviroment.Work my angles and try to get him tripped up, or perhaps catch him off balance. Establish distance and maintain it while constantly reigning jabs. Lots of them. Look for weapons/escape routes. Maybe throw something at him or dirt in his eyes. Get him frustrated. Maybe encite a roid rage. I dont know if he does them, but Im sure alot of those type of guys do. Regardless, if he is frustrated he can be outsmarted.
Attack the soft tissues. There are a few nerve strikes that could work, but the guy is a walking mountain and so penetration might not be possible in all situations. However, no matter how much he trains he has soft areas, such as the eyes or throat. Base of the skull. And yes in the groin also. Maybe.
Things you should not do. Do not find yourself trading blows. In a power versus power situation, you lose. Do not find yourself grabbed. Why would you grapple the strongest guy in the world? To say its risky would be the understatement of the year. Dont run in a straight line. If you have to run, which I hate, but if you have to run make him work for it. Hit the fences, or alleys. Run like a deer. Back and forth always changing direction.