Mariusz is a huge star in Poland (technicaly, he is a huge star everywhere
), and came 2nd in their version of 'Dancing with the stars' a couple of years ago.
He has boxing, and also high level Kyokushin experience, though I would doubt he had done any heavy sparring for some years to avoid injury in his Strongman competiton, but that is supposition on my part.
He looked scrappy, but his functional power has no doubt made it through the transition from SM to MMA, and that is going to be a problem for a lot of competitors.
I dont expect him to be unbeaten - its rare in boxing, and I suspect impossible in MMA, but he has a will to win that is freaky - his intensity in the WSM circuit is legend, and that will serve him well, and I fully expect, should he choose to focus on MMA as the next stage in his career, that he will be in the UFC before 2011, and I really dont see any reason why, as he learns the game, he cannot dominate in the same way as he has in Strongman for the last 8 years.