A mysterious, immortal donkey with a single large breast where its face would normally be. Its origins are unknown, but it is known to obstruct passages. The only way to get past it is for a member of the group to engage it by playing Sudoku so that everyone else may pass.
"Damn it, there's a tits-donkey up ahead. Now what?" Said Bill.
"Let's turn back. I fucking hate Sudoku," replied Jim.