I can not show a diagram to this puzzle, as I have forgotten the solution. It exists, though! Trust me!
Starting with a normal position, you must make a game that ends in 5 full moves (5 for white, 5 for black) in which the last move is 5...gxh1=N#. So in other words, black, on his fifth move, must capture a piece on h1 with a g2-pawn, promote it to a Knight, and checkmate white. I read somewhere that Botvinik or someone like that (someone really good) gave up on it and said it was impossible. Are you smarter than the ex-world champion?!?!?!?!?!?!?!?!?!?!?!?!?!?!?