Your first boss battle. The Tattooed Strongman will begin this fight holding a large barrel. As soon as he appears, he will toss the barrel at you. Simply walk downwards to avoid it or jump over it.
This boss can be a real pain if you don't understand how he reacts. He only has one attack, which is where he spins around in a circle with arms open wide (like Zangief of Street Fighter fame's Double Lariat move). The Tattooed Strongman will perform this attack whenever he is about to take damage, or if you get too close. After doing this attack, he will stop for a few seconds, like he's tired. During this time is when he is completely vulnerable.
Right after you hit him when he's vulnerable, make sure you move away from him because if not, he will hit you with his attack. If you let the boss chase you, you will only get yourself cornered.
The way to get him to attack is to get as close to him as possible without getting hit. Have him follow you, back step a bit to get close him, then right when he starts spinning run away. When he stops, perform a sliding kick into him, then another to escape quickly (to whichever side of him gives you more room to maneuver). If done correctly, you can even keep him in one spot (preferably the middle) and take him down in less than a minute.