While on my snow map building a tunnel over the ground (to connect two fortresses, one inside a cave system and another outside and inside a cave), I think I saw... "Him." The floor of the tunnel I was building was made of Cobblestone, while the walls and roof were made of glass. Since I was using the Realistic Texture, this made the glass more transparent. A couple of times it seemed like some of my glass was disappearing from where it had been placed. When I turned to the direction of my cave system, I saw a figure jump in a Mariolike manner, quickly leaving my sight. Due to the torches I had placed near the location of the player, I noticed he was wearing a red shirt (like my skin).