Helpmate in 4

1.Qe4 Se7 2.Qxe7 fxe7 3.Ka3 e8R 4.Ka4 Ra8.
The white knight is of no use when it comes to constructing a mate, but serves the purpose of wasting White’s first move. It turns out that the knight must be sacrificed on e7, as every other move will either check, block the queen’s path to e7 or frustrate the intended mate. Two clever points are that 1.Qe4 prevents the d4 pawn from playing a tempo move, while it is the knight’s vacation of c6 that compels White to underpromote.