Mr. Big is a character that is seen in Marble Siege 3 Update videos as the boss.
Mr. Big is shown as a large, white circle and is smiling except when injured. He has no limbs.
Mr. Big's first appearance was in Marble Siege Update Video #1, when Frigidum was using his updated spear.
His next appearance was update video #2, when Firgidum threw 3 knives, injuring Mr. Big. He lost ~300 health as a result. At the end, after the progress was done, many marbles were surrounding Mr. Big. A Poup Cannon shot Poup at him, and Neptune and Frigidum were attacking Mr. Big, who was suffering. He might be a villain, as Doc671 says in the comments: "Don't feel bad for Mr. Big. No, really. He's the manifestation of all that's wrong in the world. Don't be fooled by his innocent-looking appearance."