Solution
Try to figure out the solution yourself before checking the analysis board!
1. The Draw and The Mate
2. Why does one of the pawn promotions not lead to a mate?
If we try to make the same moves in b8=Q as in the a8=Q line, black has a unique defensive resource.
Black was winning but had just blundered the game by promoting one of their pawns. One pawn promotion leads to a draw, but another allows mate in 15 by white. Find out which is which!