Duncan The Original. World's #1. For more than 8 decades Duncan's performance and quality has been something you can depend on in a toy. Mental Block is for 2 to 4 players. This Brain twister is Super Easy to learn but a Challenge to win! Not like 2 dimensional games this has you climbing walls and going around corners, Simply be the first player to connect 4 pegs in row and win! Pegs store inside the cube and it also comes with more game play variations inside the manual!