This achievement requires that you finish a multiplayer crossword (in any game mode) in first place. First place is earned by having the maximum score. Your score is shown beneath your gamerpic under the puzzle. There must be at least one other player in the game to be considered a multiplayer game. They do not need to be present at the end of the puzzle. In fact, neither do you, but you must have the highest score. Either join another player's Public puzzle, or create your own and make it Public, rapidly filling out the puzzle and racking up the points. This unlocks at the puzzle completed screen.