The most opponents tacked by a blindfolded player is 46. This was achieved by German Master Marc Lang in Sontheim-an-der-Brenze, Germany, on 27 November 2011. The simultaneous match went on for 21 hours and ended with Lang winning 25 games, drawing 19 and losing two.
In blindfold chess matches, the player is told what move his opponent has just made, but has no ability to go back and see what they did before. This means that the player has to keep a mental image of the board, complete with the position of every piece, in order to make sound tactical decisions. Multiple simultaneous games represent a immensely difficult test of memory and skill.
Marc Lang’s rating is 2,300, and most of his opponents were rated 1,700 or lower (weak amateur club standard), but they could all see the board.